MODERN ELECTfflCAL^ 
CONSTRUCTJON I 




Book Ani^ 



Copgtitl^". 



|: 



COPYRIGHT DEPOSITS 



&113IS13 



MODERN 

Electrical Construction 

A RELIABLE, PRACTICAL GUIDE FOR THE 
BEGINNER IN ELECTRICAL CONSTRUCTION 
SHOWING THE LATEST APPROVED METHODS 
OF INSTALLING WORK OF ALL KINDS AC- 
CORDING TO THE SAFETY RULES OF THE 

National Board of Fire Underwriters 



By 

HENRY C. HORSTMANN 
VICTOR H. TOUSLEY 

Author i of ^^ Modern Wiring Diagrams and Descriptions^'' 



31Uu0trateu 




CHICAGO 

FREDERICK J. DRAKE & CO., PUBLISHERS 

1905 






LIBRARY of OON'iKtSS 

JUN 5 iyui) 
/033 9/ 

JOPY B. 



COPYRIGHT, 1904 

BY 

HORSTMANN AND TOUSLEY 



PREFACE 



In this volume an attempt is made to provide the beginner 
in electrical construction work with a reliable, practical guide; 
one that is to tell him exactly how to install his work in ac- 
cordance with the latest approved methods. 

It is also intended to give such an elaboration of "safety 
rules" as shall make the book valuable to the finished work- 
man as well. To this end the rules of the "National Electrical 
Code" of the National Board of Fire Underwriters have been 
given • in full, and used as a text in connection with which 
there is interspersed in the proper places a complete explana- 
tion of such work as the rules may apply to. This method of 
teaching and explaining practical electricity may at first glance 
seem somewhat haphazard, but it resembles very closely the 
actual method by which the most successful, practical work- 
men have learned the trade. It is thought that explanations 
pertaining directly to the work in hand will be more deeply 
considered and more likely to be fully comprehended than 
explanations necessarily more abstract. 

It should be noted that, while the rules published in the 
"National Electrical Code" are standard and work done in 



conformity with them will be first-class, several of the larger 
cities have ordinances governing electrical work which con- 
flict in some details with these rules. Workers in such cities 
should, therefore, provide themselves with copies of these 
ordinances (usually obtainable without charge), and compare 
them with the rules given in this work. It is necessary for 
the electrical worker at all times to keep himself posted, for 
safety rules are liable to change. 

The tables concerning screws, nails, number of wires that 
can be used in conduit, etc., are especially prepared for this 
volume, and give to it particular value for practical men. 

The Authors. 



CHAPTER I. 
The Electric Current. 

It is quite customary and convenient to speak of that 
agency by which electrical phenomena, such as heat, light, 
magnetism, and chemical action are produced as the electric 
current. In many ways this current is quite analogous to cur- 
rents of air or water. Just as water tends to flow from a 
higher to a lower level, and air from a region of greater 
density or pressure to one of lesser density, so do currents of 
electricity flow from a region of high pressure to one of low 
pressure. Currents of electricity form no exception whatever 
to the general law of all action, which is along the lines of 
least resistance. It must not be understood, however, that 
electricity actually flows in or along a conductor, as water 
does in a pipe, and the analogy must not be carried too far, for 
the flow of water in pipes is influenced by many conditions 
which do not influence a flow of electricity at all, and vice 
versa; there are conditions surrounding conductors, which 
influence the flow of electricity which do not affect the flow 
of water. 

Above all, let it be understood that electricity is not inde- 
pendent energy, any more than the belt which gives motion 
to a pulley is. In other words, it is not a prime mover, it is 
simply a medium which may be used for the transmission of 
energy, just as the belt is used. To use electricity as a 
medium for the transmission of energy, it must be, we may 
say, compressed, or, to use a more properly technical expres- 
sion, a difference of potential or pressure must be created in 
a system of conductors. This is very similar to the use of air 



8 MODERN ELECTRICAL CONSTRUCTION. 

for power transmission; this must also be compressed so that 
a difference of pressure exists within a system of piping. 

It is the flow of electricity or air which takes place when 
switches or valves are operated and which tends to equalize 
this pressure, i. e., flow from high to lovV pressure, that does 
our work. The real energy, however, (so far as we are con- 
cerned), to which we must look for our initial motion in 
either case is derived from the coal which generates steam; 
or, in the case of water-driven machinery, the rays of the sun 
which evaporate water, allowing it to be carried to higher 
levels, from whence it flows downward over dams ar.d falls 
on its way back to the lowest level. In the batters', the real 
energy is that of chemical action, which is transformed into 
electrical energy. 

The flow of current can take place only in a systenx of 
conductors which usually, for convenience, are made in the 
form of wires. The current for practical purposes m.ay be 
considered as flowing along such wires only. It is not, how- 




Figure 1 

ever, necessary that these wires should be of any particular 
size, or consist all of the same material. In an electric bat- 
tery, part of the circuit consists of the liquid contained within 
the battery; the rest being made up usually of wire. In an 
incandescent light circuit part of the circuit consists of the 



ELECTRIC CURRENT. ^ 

lamp filament (usually carbon), while the balance of the cir- 
cuit consists of copper wire. 

The flow of current is also said to have a certam direction; 
that is, it is noticed that many of its effects are reversed when 
the terminals of the battery are reversed. Referring to Fig. 
1 which shows a battery of three cells, the current flows from 
the copper element at bottom of jar 1, along the wire to the 
zinc element at top of jar 2, thence through the liquid to the 
copper element at bottom of jar 2, and from there to the zinc 
at top of jar 3, etc., and finally through the wire a back to 
the starting point. Within the battery the current flows from 
the zinc to the copper and the decomposition of the zinc gen- 
erates the current. In the wire outside of the battery the cur- 
rent flows from the copper to the zinc as Indicated by arrows. 
The combination of battery and wire is known as an electric 
circuit. The current will flow in this circuit only while it 
is complete, that is while each wire connects to its proper 
place as shown. If any wire is disconnected, the current flow 
v.-ill cease. Such a circuit is sa^id to be open, but when all 
connections are properly made it is said to be closed. 

Work can be obtained from a flow of current in many 
ways. If the current be forced to flow over a wire which is 
very small in proportion to the current carried, it will be 
heated thereby and finally melted if the current is excessive. 
This is how electric light is obtained. 

If a wire carrying current be wound many times about 
an iron bar this bar becomes a magnet ; that is, while the cur- 
rent is flowing around it, the bar has the power to attract 
other objects of iron or steel. The bar if made of well an- 
nealed iron will be a magnet while current is flowing around 
it, but will cease to be magnetic whenever the current flow 
ceases. Upon this fact the operation of electric bells, telegraph 
instruments and motors is based. 

If a current of electricity flow through a properly arranged 



10 MODERN ELECTRICAL CONSTRUCTION. 

"bath," one of the plates will be gradually consumed and the 
other increased in weight. This effect is made use of in 
electro-plating, etc. If the jar contains water slightly acid- 
ulated and the current flows through it, the water will be 
decomposed and oxygen and hydrogen gas will be formed. 
This and many kindred effects are daily used in thousands of 
chemical laboratories. 

If a wire carrying an electric current be placed very close 
to another wire forming a closed circuit, a wave of current 
will be induced in that wire every time the current in the 
other is made or broken, i. e., whenever it starts to flow or 
stops flowing. This fact forms the basis of the alternating 
current transformer. 

All of these facts are used sometimes together, sometimes 
singly in measuring the electric current. 



Conductors and Insulators. 

Electrically speaking, all substances are divided into two 
classes. They are either conductors or insulators. By thi>? 
is not meant that some substances can carry no current at 
all, for, as a matter of fact, there is no such thing as either a 
perfect conductor or a pecfect insulator. A current of elec- 
tricity can be forced through any substance, provided the pres- 
sure (E. M. F.) be made great enough, and there is no easier 
path open to the current. The two terms, conductor and 
insulator, are relative terms and must be understood simply 
to mean that the electrical resistance of a good conductor is 
infinitesimally small as compared to that of a good insulator. 
The lower the specific resistance of any substance, the better 
its conducting qualities ; the higher the specific resistance of 
any substance, the better will be its insulating qualities. 

At the left is given a list of good conductors, in the order 
of their conductivity, the figures representing the relative con- 



ELECTRO- MOTIVE-FORCE. 11 

ductivity of these metals. A list of insulators is given at the 
right; all of these are more or less affected by moisture, los- 
ing their insulating qualities when wet. 

Silver 100.0 Dry air. Fiber. 

Copper 94.0 Rubber. Wood. 

Gold ; 73.0 Paraffin. Shellac. 

Platinum 16.6 Slate. 

Iron 15.5 Marble. 

Tin 11.4 Glass. 

Lead 7.6 Porcelain. 

Bismuth 1.1 Mica. 



Pressure or Electro-Motive Force. 

Currents of electricity flow only in obedience to electrical 
pressure. This pressure is measured and expressed in volts, 
the unit of electrical pressure being the volt. If we speak 
of water or steam pressure, we speak of it in pounds, the 
pound being the unit of measurement. In speaking of elec- 
trical pressure we refer to it as of so many volts. There is no 
direct connection between the pound and the volt, but each 
in its place means about the same thing. 

The volt is defined as that difference of potential (pres- 
sure) that must be maintained to force a current of one 
ampere through a resistance of one ohm. 

If we have a resistance greater than one ohm and wish to 
send a current of one ampere through it, we can do so by 
increasing the pressure or voltage, as it is termed, accordingly. 
The current flowing in a circuit can also be reduced by reduc- 
ing the voltage. 

The ordinary incandescent lamps operate at about 110 
volts pressure, although some are built for 220 volts. An elec- 
tric bell requires about 2^ volts (a battery of 2 cells) for 
proper operation. 



12 MODERN ELECTRICAL CONSTRUCTION. 

Resistance. 

We have seen that a flow of current always takes place 
along or in a conductor. Every conductor, no matter how 
large or small it may be, offers some resistance to this ilow 
of current just as the water pipe offers more or less resistance 
to the flow of water. This resistance may be measured and 
expressed in ohms; the unit of electrical resistance being the 
ohm. The ohm is defined as that resistance which requires a 
difference of potential of one volt to send a current of one 
ampere through it. If we should desire to send a greater cur- 
rent through any resistance, we can do so by increasing the 
pressure, just as we can increase the flow of water in a pipe 
by increasing the pressure or head of water in the tank that 
supplies it. If the pressure is fixed we can decrease the 
current by using a wire of greater resistance or increase it by 
using wires of lesser resistance. 

The ohm is the resistance of a column of mercury 106.2 
centimeters long (about 3^ feet) and one square millimetre 
(about .0015 sq. in.), in cross-section, at the temperature of 
melting ice. 

The resistance of a No. 14 copper wire about 380 feet long 
is equal to one ohm. 

The resistance of all conductors increases directly as the 



3 

Figure 2 

length and decreases as the cross-section increases. In Figure 
2 the resistance of the two bars of copper is exactly equal. 
Bar No. 1 having a cross-section of 4 square inches and being 
4 feet long, while bar No. 2 has a cross-section of only 1 
square inch and is only one foot long. If bar No. 1 were 



OHMS LAW. ' 13 

reduced to a cross-section of 1 square inch, it would become 
16 feet long and would have a resistance 16 times as great as 
that of bar No. 2. 

Current. 

The electric current is the result of electrical pressure 
(volts) acting through a resistance, and is measured in 
amperes, the ampere being the unit of current strength. The 
ampere is defined as that current which will flow through a 
resistance of one ohm when a difference of potential or pres- 
sure of one volt is maintained at its terminals. 

The ampere expresses only the rate of flow, not the quan- 
tity. Knowing the amperes if we would know the quantity, 
we must multiply by the time that the rate of flow continues. 
Ihe rate of flow is analogous to the speed of a train; unless 
we know how long the train is to maintain a certain speed, we 
have no idea how far it is going. 

Quantity in electricity is measured in coulombs. The 
coulomb is the quantity of current delivered by a flow of one 
ampere in one second. 

Ohm's Law. 

Ohm's law expresses the relation of the three principal 
electrical units to each other and forms the basis of all elec- 
trical calculations. 

This law states that in any electric circuit (with direct 
current) the current equals the electro-motive force divided by 
the resistance. The current, we have already seen, is the 
medium which does our work. Current flow, we see from this 
law, can be increased either by increasing the electro-motive 
force, or electric pressure, which causes the flow; or by 
decreasing the resistance which tends to prevent current flow. 
Expressed in symbols it is this : I=E/R ; where I stands for 



14 MODERN ELECTRICAL CONSTRUCTION. 

current, E, for electro-motive force, and R for resistance. ■ If, 
as an example, we have an electro-motive force (which we 
shall henceforth designate by the customary abbreviation, E. 
M. F.) of 110 volts and a resistance of 220 ohms, the resulting 
current will be 110 divided by 220=^ ampere, being approxi- 
mately the current used in a 16 cp. incandescent lamp at 110 
volts. Thus it will be seen that by a very simple calculation 
we can find the current flow in any conductor if we but know 
the E. M. F. and the resistance of that circuit. 

This formula can also be used to find the E. M. F., if we 
know the value of current and the resistance, since E divided 
by R=I; I times R must equal E. If the current and resist- 
ance are known, we need only to multiply them together to find 
the E. M. F.; IXR=E. Knowing the current and E. M. F., 
we can find the value of the resistance by dividing the E. M. 
F. by the current ; E/I=R. 

As a practical application of these formulas : If we wish 
to know how much current a certain E. M. F. can force 
through a certain resistance, we must divide the E. M. F. 
(volts) by the resistance (ohms.) If we wish to know what 
E. M. F. (volts) will be necessary to force a certain cur- 
rent (amperes) through a certain resistance, we need only 
multiply the current (amperes) to be obtained by the resist- 
ance in ohms. If we wish to know how much resistance 
(ohms) must be placed in a circuit to keep down the current 
flow to a certain limit, we need only divide the E. M. F. 
(volts) by the desired current (amperes) ; the result will be 
the value in ohms of the required resistance. 

Power. 

The power consumed or transmitted in an electric cir- 
cuit equals the product of the volts and amperes; pressure 
and current. 



POWER, 15 

To find the power of a steam engine, we must know the 
pressure of the steam and the quantity used; the power con- 
tained in the water of a dam depends upon its vohime and its 
head. The power we can obtain from the wind depends upon 
its speed and the surface we expose to it which also measures 
the quantity. 

All of these cases are analogous and similar. Power ex- 
presses the rate of doing work, thus the rate of work is the 
same whether we are lifting one pound at the rate of 100 
feet per minute, or 100 pounds at the rate of one foot per 
minute. The unit of electrical power is the watt. It is the 
power expended in an electric circuit when one ampere flows 
through a resistance of one ohm, or when a difference of 
potential of one volt is maintained in a circuit having a resist- 
ance of one ohm. In an electric light circuit, for instance, 
as far as the power is concerned, it is immaterial whether 
each lamp requires 110 volts and 5-^ ampere, or 55 volts and 
one ampere, or 220 volts and }i ampere. The power (watts) 
expended in an electric circuit is always equal to the volts 
multiplied by the amperes; thus, one ampere at 1,000 volts 
is equal to 100 amperes at 10 volts, or to 200 amperes at 5 
volts. In any power transmission whenever the pressure 
(volts) is lowered, the current (amperes) must be increased 
or the power (watts) will fall off, and, on the other hand, 
whenever the pressure is increased the current may be 
decreased. 

Instead of multiplying volts by amperes, we can find the 
power in an electric light circuit by multiplying the current by 
itself and then by the resistance ; or the E. M. F. by itself and 
divide by the resistance. 

Thus knowing the volts and the amperes, we use the 
formula E X I=W. Knowing only the amperes and the 
ohms,- we may use the formula, P X R = W; and lastly, 



16 



MODERN ELECTRICAL CONSTRUCTION. 



knowing only the volts and ohms, we use the formula, 
EVR = W. 

In the above E stands for E. M. F., or volts; I for current 
or amperes; and R for resistance or ohms. 



Divided Circuits. 

Currents of electricity always flow along the paths of 
least resistance just as currents of water do. Water, it is 
well known, will not flow over the top of a mill dam while 



\aaaaa/\aa/ 



Figure 3 

there is an opening alongside of it through which it can flow. 
If a barrel of water be provided with two openings, one 
large opening and one small, a much larger quantity will 
flow out through the large opening than through the small. 
This is because the resistance to the flow of water of the 
large opening is so much less than the resistance of the 
small opening. 

An electric current will act in just the same way; the 
conductor having the lesser resistance will carry the greater 
current. If we know the resistances of the different paths 
open to a certain current we can determine to a nicety how 
much current will flow in each. In Figure 3, which repre- 
sents diagramatically a battery of two cells and an electric 
circuit, the resistance of the two paths, a and b, is equal to 



DIVIDED CIRCUITS. 17 

10 ohms each, and the current will divide equally between 
them. If the resistance of a were 5 ohms, and that of b, 
10 ohms, two-thirds of the total current would pass through 
a and the one-third through b. 

In all such divided circuits, the current is always in- 
versely proportional to the resistance and the simplest way 
to find the current in each is to add the resistances of the two 
circuits ; for instance as above, 5 plus 10 equals 15 ; now 
5/15 of this current will flow through the 10 ohms and 10/15 
of the current will flow through the 5 ohms. 

To determine the combined resistance of the two wires, 
a and b, we need simply to consider them as made into one 
wire. If they are both alike, they would, if made into one 
wire, be twice as large as either one is at present, and would 
then have only one-half as much resistance as either one had 
before ; for the resistance of any conductor increases directly 
as its length, and decreases as the cross-section increases. 
The combined resistances of any two conductors can be found 
by multiplying their two resistances together and dividing 
this product by their sum. Thus, again taking the value 
of a and b as 10 ohms each, 10X10 equals 100, this divided 
by 10 plus 10 equals 5, which is the combined resistance of the 
two. 

If we have a large number of branch circuits as shown in 
Figure 4, which represents diagramatically an incandescent 

mnmsB 

Figure 4 

electric light circuit of 12 lights (which is equal to 12 separate 
circuits, since each lamp really forms a circuit by itself), we 
can find the joint resistance of the 12 by proceeding as before; 
that is, multiplying together the resistance of the first and 




18 MODERN ELECTRICAL CONSTRUCTION. 

second lamp and dividing by the sum of these resistances ; next 
take the result so obtained (which is the combined resist- 
ance of the first two lamps) and with it multiply the resist- 
ance of the third lamp and divide by the sum as before. By 
repeating this operation and always treating the joint resist- 
ances already found as one circuit, the joint resistance of any 
number of such circuits can be found. Another and a very 
much quicker way consists in using the following formula : 
The joint resistance of any number of parallel circuits is 
equal to the reciprocal of the sum of the reciprocals. The 
reciprocal of any number is 1 divided by that number. If we 
have three circuits, having respectively 10, 20, and 30 ohms 
resistance, we proceed in the following way: The reciprocal 
of 10 is 1/10, of 20, 1/20, etc., the joint resistance, there- 
fore, is 1/10 plus 1/20 plus 1/30 equals 11/60, and 1 divided 
by this number which is 5 5/11. 

These methods are only necessary when the resistances 
are of different values. When all of them are alike, as is 
usual with incandescent lights, the resistance of one lamp 
needs only to be divided by the number of lamps to find the 
joint resistance. Thus, supposing each of the 12 lamps to 
have a resistance of 220 ohms, the joint resistance of the 
circuit would be 220/12=181/3. 



CHAPTER II. 
Electric Bells. 

We are now in a position to apply the electrical laws we 
have just discussed practically, and for this purpose may 
take up electric bells and bell circuits. 

Figure 5 shows an electric bell, push button and battery, 
all connected up and complete. The action of the bell when 




Figure 5 



fully connected is as follows : Pressing the push button 
closes the circuit and current at once flows from the carbon 
pole marked + through the push button to the binding post 
A on the bell frame, thence along the fine wire W to the 
iron frame-work supporting the armature, B. This frame- 



20 MODERN ELECTRICAL CONSTRUCTION. 

work is in electrical connection with B. The armature, B, 
is provided with contact spring S, which normally rests 
against the adjusting screw, C. The current now passes from 
the contact spring to the adjusting screw and from it to the 
wire wound on the magnets, M, around the many turns of 
wire to the binding post, D, and back to the zinc pole of the 
battery marked — . 

The current circulating many times in the wire wound on 
the spools of M makes the iron cores magnetic so that they 
now attract the armature B. When this armature is at- 
tracted, it moves towards the magnets, M, and carries the 
small contact spring with it, thus breaking the connection be- 
tween C and S. 

This stops the current flow and the magnets, M, are at 
once demagnetized, thus releasing the armature B, which 
flies back and again clores the circuit at CS, this causes the 
armature to be attracted again and once more the circuit is 
broken. In this way the armature is made to strike the gong 
continuously while the circuit is kept closed at the push button. 
When the button is released, the circuit is permanently open 
and the bell at rest. 

In the figure there is shown only one cell, this, if a good 
form is selected, is sufficient for a new bell if the circuit is 
not long. When, however, the bell is used much the contact 
points are eaten away by the little sparks occurring every time 
the bell breaks the circuit. Dirt is also likely to gather on 
them and prevent good contact being made. Both of these 
factors add resistance to the circuit, and consequently 
lessen the current flow. 

We have seen before that the current equals the E. M. 
F. divided by the resistance, and in order to obtain the 
necessary current flow to operate the bell, we may either 
clean the contact points to lessen the resistance, or increase 
the E. M. F. by adding another cell in series with the first. 



ELECTRIC BELLS. 



21 



The latter expedient is by far the better, because it gives 
us a httle surplus of power which is very useful to over- 
come variations in adjustment of the contact spring, loose 
contacts, dirt, etc. We should avoid using too many cells 
as well as not enough. If too many cells are used, there 



Q 






d. 



Q 

a 



»! 



jn 



Figure 6 

will be much unnecessary damage done to contact points by 
the larger sparks. 

If the circuit is very long, the great length of wire will 
also provide additional resistance. This can be overcome in 
two ways, by increasing the E. M. F. as above, or by using 
larger wires. We have already seen that the larger the wire, 
the less will be its resistance. It is common practice to use 



22 MODERN ELECTRICAL CONSTRUCTION. 

No. 18 copper wire for all ordinary distances and for single 
bells. With large bell systems, it is customary to use No. 16 
or 14 for the main wire, which leads to all of the bells and 
may be called upon to supply several bells at the same time. 
Figure 6 shows a diagram of such a system and in case the 
three push buttons are used at the same time, three times as 
much current will flow in the main or battery wire a as in 
either of the other wires. 

We have seen before that currents of electricity divide 
among different circuits in the inverse ratio of their resist- 
ances. In other words, the circuit having the least resistance 
will carry the most current. If our bell system, Figure 6, 
be "grounded" at the two points x and y (i. e., bare wire in 
contact with metal parts of buildings which are connected 
together) the current instead of flowing through the longer 
circuit and the bell, will flow through the short circuit and 
leave it impossible to operate the bells. If the contacts, at 
X and y are poor, i. e., of high resistance, only a small part 
of the current will leak from one to the other. In such a 
case, the bells may work properly, but the battery will soon 
run down and there is a strong likelihood that one of the 
wires will be eaten away through electrolytic action. To 
prevent troubles of this kind, bell wires should be well in- 
sulated and kept away from pipes or metal parts of building. 
Damp places should also be avoided and special care is 
recommended for the battery wire a, Figure 6. For further 
information concerning diagrams, etc., of bell circuits the 
reader is referred to Wiring Diagrams and Dcscriptidns by 
the authors of this work, Fred J. Drake & Co., Chicago. 

Bell wires are usually run along base boards, over picture 
mouldings, etc., in some cases they are also fished as explained 
further on. Batteries should be located in cool, dry places, 
where they are not liable to freeze, and where they are 
readily accessible as they must be kept nearly full of water 
and must be recharged from time to time. 



23 



The Telephone. 



The principle and action of the Bell telephone can be best 
explained by reference to Figure 7. In this figure, A repre- 
sents the transmitter, and B, the receiver. The essential 
parts of the transmitter are : the diaphragm, a; an electric 
circuit, containing a battery, b, and consisting of the wires, 
c, c^ and partly wound upon an iron core, d. 

This electric circuit, it will be seen from the figure, con- 
nects with one pole to the diaphragm, a, and with the other 
to a small metal plate, e. Between the diaphragm, a (which 
is a plate of very thin iron), and the plate, e, there are many 
small pieces of carbon which complete the circuit. When 
now a party speaks into the mouthpiece of the transmitter, 




Figure 7 



the sound waves cause the diaphragm, a, to vibrate; the rate 
of vibration and character of the vibrations being an exact 
duplication of the voice speaking into it. These vibrations 
cause the small pieces of carbon between the diaphragm and 
the back plate to be alternately compressed and allowed to 
expand. Now the resistance of these carbon pieces is de- 
creased as they are tightly pressed together, and again in- 
creased when the pressure is released. Therefore the cur- 
rent of electricity flowing through them varies continuously 
while the diaphragm is in motion. 

This varying current circulates around the lower part 
of the iron core, d, and the two windings upon it form an 



24 



MODERN ELECTRICAL CONSTRUCTION. 



ordinary induction coil. Every variation of current strength 
in the circuit of the transmitter is by means of it reproduced 
in the circuit of the receiver, B. 

The essential parts of the telephone receiver are : The 
diaphragm /, very similar to that of the transmitter, the two 
magnets, g, and the electric circuit coming from the induction 
coil of the transmitter. The electric circuit, we have already 
seen, is traversed by electric currents exactly like those that 
flow in the circuit of the transmitter. These currents pass 
around electro-magnets, g, and attract the diaphragm, /, 
more or less strongly in proportion to the varying degrees of 
current strength. 

In this manner the diaphragm, /, of the receiver is made 
to vibrate in exact unison with that of the transmitter, and 
thus to reproduce exactly the sounds given to the trans- 
mitter. 

The transmitter is not absolutely necessary for the re- 




Figure 8 

ceiver can be used as such, and in fact was so used at first. 
Lines of short distances can be operated without transmit- 
ters, but the speech will not be as plain. 



INDUCTION COIL. 



25 



Figure 8 is a diagram of the connections of two telephone 
instruments together with the necessary call bells. When the 
lines are not in use, the receivers, a, are hanging on the 
hooks, h, holding them down as shown by dotted lines. This 
leaves the circuit complete through the earth, g, magneto 
generator, e, bell /, line i and duplicates of these parts at the 
right. When now the magneto generator is operated both 
bells will ring. When the receivers are removed, a spring 
forces the hook upwards making the connection shown in 
solid lines. This closes the battery circuit which must be 
open when the instrument is not in use or the battery will 
run down. 

The talking circuit is now complete from earth, g, through 
the receiver, a, induction coil, b, line i, and duplicates of these 
parts at the right. 



The Induction Coil. 

Figure 9 is a diagramatic illustration of an induction 
coil as used mostly by medical men. Such an instrument 




Figure 



consists of an iron core, B, usually made up of a number 
of soft iron wires ; and two electrical circuits insulated from 
each other, and terminating in the two pair of binding posts, 
A and D. Of these two circuits A consists of a short length 



26 MODERN ELECTRICAL CONSTRUCTION. 

of comparatively heavy wire wound upon the iron core, and 
is known as the primary coil. D is a similar coil, but usually 
consisting of many more turns of wire, and the wire is also of 
much smaller gauge and is known as the secondary coil. 

The operation is as follows : A battery is connected to the 
binding posts. A, and current begins to flow in the circuit. In 
this circuit is an interrupter or vibrator, E, constructed 
similarly to the one described in connection with the electric 
bell. As current flows through the primary coil, it mag- 
netizes the core, B, and this attracts the armature, E, causing 
it to break the connection between itself and the adjusting 
screw. As this connection is broken, the current in A ceases 
to flow, the core is de-magnetized and the armature again 
connects with the adjusting screw. This action is repeated 
just as in the electric bell, and in consequence the core B, 
is rapidly magnetized and de-magnetized. 

Every time the core, B, is magnetized a current of electric- 
ity, lasting, however, only an instant, is induced in the second- 
ary coil, D. The magnetism in the core is caused by a cur- 
rent of electricity circulating around it, and currents of 
electricity are in turn produced by this magnetism in the 
other or secondary coil. 

This method of producing electric currents is known as 
electro-magnetic induction, and currents so produced are said 
to be "induced" currents, hence the name induction coil. The 
currents so induced are alternating, that is, changing in 
direction. At the "making" of the primary circuit, the cur- 
rent in the secondary coil is in a direction which opposes the 
magnetization of the core by the primary current; at the time 
of "break" in the primary circuit, the induced current will be 
in the opposite direction. 

The tube, C, is movable and may be slipped entirely in over 
the iron core, or withdrawn entirely. If it is in, the currents 
which were before being induced in the secondary wires are 



BATTERIES 



27 



now induced in the metal of the tube and consequently the 
effect on the secondaries is very much reduced. 

The energy in the primary and secondary coils is always 
equal. If the two coils have the same number of turns, the 
currents and electro-motive forces are exactly alike. If the 
secondary coil has more turns of wire than the primary, 
the induced E. M. F. in it will be greater, but the current 
will be smaller and vice versa. The induction coil is very 
similar to the alternating current transformer, the main 
difference being that the transformer does not have an in- 
terrupter since the current supplied to it is itself constantly 
alternating. 

Batteries. 



Currents of electricity for commercial purposes are pro- 
duced either by dynamo electric machines or by batteries. 

A "battery" is the name given to a number of cells con- 
nected together so as to produce a current greater than one 





Figure 10 



Figure 11 



cell alone could produce. Figure 10 shows one cell of a kind 
that is generally used only intermittently, as for instance with 
door-bells. When the bell is not ringing the battery is idle. 



28 MODERN ELECTRICAL CONSTRUCTION. 

This style of cell is very useful for such work, but entirely 
useless for work requiring current continuously." The cell 
consists of a glass jar which is filled about % full of water 
in which a quantity of sal-ammoniac is dissolved. Immersed in 
this solution is a carbon cup or center, which forms the 
positive or + pole of the cell, and a zinc rod, carefully 
separated from the carbon by a rubber washer at the bottom 
and a porcelain tube at the top. So arranged, the current tends 
to flow, in the battery, from the zinc to the carbon and if the 
zinc and carbon outside of the cell be joined by a piece of 
wire or other conductor of electricity, the current will flow 
in the external circuit, from the carbon back to the zinc. If 
the zinc and carbon are not joined by a conductor of electric- 
ity there will be no current flow, but merely an electrical pres- 
sure tending to send a current. Each cell of this kind has 
an electro-motive force of about 1.4 volts. This is not suffic- 
ient for general use in connection with bells, etc., and in 
order to obtain greater current strength a number of cells 
are connected together in series as shown in Figure 11. 

This figure shows a different kind of cell, but will never- 
theless illustrate the method of connecting cells in series; 
which is, to connect the carbon or copper pole of the first 
cell to the zinc of the second, and again the carbon pole of the 
second to the zinc of the third, continuing in this way through 
all of the cells. Thus connected, all of the electro-motive 
forces act in one direction and if we have twelve cells each 
of an electro-motive - force of 1.4 volts, we obtain a total 
electro-motive force to apply on our work of 12 X 1.4 or 16.8 
volts, 

ShoulQ vve, however, connect six of the twelve cells as 
above, and then accidentally connect the other six in the 
opposite direction, that is, the zinc of the sixth cell to the 
zinc of the seventh, and then continue in this order, we should 
obtain no current whatever; six of our cells would tend to 



BATTERIES. 29 

send current in one direction and six in the other, so that the 
result would be nothing. Should ten cells be properly con- 
nected to send current in one direction and two connected 
to oppose them, the net electro-motive force would be 10 X 1.4 
minus 2 X 1.4, which is 11.2. The ten cells would force current 
through the other two in the opposite direction. 

The electro-motive force of a cell is independent of its 
size, that is, a very small cell would set up just as high an 
electrical pressure as a very large one made of the same 
material. A large cell is, however, capable of delivering a 
much stronger current because its own resistance to the cur- 
rent flow is much less than that of a small cell. Large cells 
will, therefore, in most cases give very much better service 
than small ones. Especially in cases where considerable 
current is required as in electric gas-lighting and annunciator 
work, where it is always possible that two or three bells or 
fixtures may be called into action at the same time. 

In setting up and maintaining sal-ammoniac batteries, the 
following general rules should be observed : 

Use only as much sal-ammoniac as will readily be dis- 
solved; if any settles at the bottom it shows that too much 
has been used. Keep your battery in a cool place, but do 
not allow it to freeze. See that the jars are always about 
^ full of water. 

Keep the tops of glass jars covered with paraffir. to 
prevent salts from creeping. 

The battery should never be allowed to remain in action 
(i. e., send current) continuously, or it will run down. If 
it has been run down through a short circuit or other cause, 
it should be left in open circuit for several hours; it will then 
usually ''pick up" again. 

The so-called dry-batteries are made up of about the 
same material, but applied in form of a paste. They are 



30 MODERN ELECTRICAL CONSTRUCTION. 

suitable for the same kind of work and especially handy for 
portable use. 

For continuous current work, such as telegraphy, for 
instance, the kind of battery shown in Figure 11 is generally 
used. The electro-motive force of this style of battery is a 
little less than that of the sal-ammoniac battery and its re- 
sistance is considerably greater. 

Therefore, it is not well adapted for work requiring con- 
siderable current strength. Bells, telegraph instruments, etc., 
to be used with this battery require to be specially designed 
for it; the current being less in quantity must be made to 
circulate around the magnets many more times in order to 
fully magnetize them. 

The sal-ammoniac batteries cannot be used continually or 
they will run down ; this battery must be kept at work always 
or it will deteriorate. 

This style of cell is known as the crow-foot or gravity 
cell, the action of gravity being depended upon to separate 
the essential elements of the solution. 

To set up this battery, the zinc crow-foot is suspended 
from the top of the glass jar as shown. The other element 
of the cell consists of copper strips riveted together and 
connected to a rubber-covered wire shown at the left of each 
cell, Figure 11. This copper is spread out on the bottom of 
the jar and clear water poured in until it covers the zinc. 
Next drop in small lumps of blue vitriol, about six or eight 
ounces to each cell. 

The resistance may be reduced and the battery be made 
immediately available by drawing about half a pint of the 
upper solution from a battery already in use and pouring it 
into the jar; or, when this cannot be done, by putting into 
the liquid four or five ounces of pulverized sulphate of zinc. 

Blue vitriol should be dropped into the jar as it is con- 
sumed, care being taken that it goes to the bottom. The 



BATTERIES. 



31 



r. 



n 



need of the blue vitriol is shown by the fading of the blue 
color, which should be kept as high as the top of the copper, 
but should never reach the zinc. 

A battery of this kind when newly set up should be short 
circuited for a few hours, that is, a wire should be con- 
nected from the zinc at one end of the battery to the copper 
at the other. 

There are many styles of batteries and different chemicals 
are used with them. The two kinds above described are, 
however, the most used. The methods of connecting is in 
all batteries the same. 

Figure 12 shows a diagram of a battery connected in 
series ; the long thin lines repre- 
sent the copper or carbon pole 
from which the current flows in 
the external circuit and the short 
thick lines represent the zinc from 
which the current flows toward 
the copper inside of the cell. 
If we have a circuit of low resistance to work through 
and desire to increase the current, we may group our cells as 
shown in Figure 13, where two 
sets are in parallel. This arrange- 
ment will give a stronger current, 
but it is necessary to see that both 
— I — - — I — groups of cells have the same 

1^ I" IV ^ electro-motive force; if they have 

Figure 13 ^^^^ ^^^ higher one will send the 

current through the lower. If the two batteries are not con- 
nected with similar poles together, they would be on short cir- 
cuit, and no current could be obtained in the external circuit. 



Figure 12 



^ 



CHAPTER III. 

Wiring Systems. 

There are numerous systems of electric light distribution. 
The oldest and the first to come into general use is shown 
diagramatically in Figure 14. This is the series arc system. 
In this system the same current passes through all of the 
lamps ; and as more or less lamps are required the E. M. F. 
of the dynamo must be correspondingly increased or dimin- 





N/ 


\/ 


\/- 


\y 


\y 


\/ 


l-H 


/\ 


/\ 


y\ 


y\ 


y\ 


/ 


\ 


















^ 
















|| 


\^ 


\^ 


N/ 


N/ 


\y 


\ 


/ 




/\ 


/\ 


— /X 


/\ 


/\ 


/ 


s 



Figure 14 

ished. This is accomplished by means of an automatic 
regulator connected to the dynamo. 

The current used with this system seldom exceeds ten 
amperes and large wires are never required. This system is 
best suited for street lighting where long distances are to be 
covered. 

In these diagrams, D represents the dynamo, and F, 
the "field" coils of the dynamo. With constant current 
systems the "fields" are usually in series with the armature 
of the dynamo, as shown in Fig. 14, and the lamps, so 
that the same current must pass through all. With constant 



WIRING SYSTEMS. 



33 



potential systems, the field coils are generally independent of 
the rest of the circuit. With such systems the current used 
in the circuit is so variable that it cannot be used in the 
fields. 

Another system, known as the multiple arc or parallel 
system, is shown in Figure 15. In this system the E. M. 
F. never varies, but the current is always proportional to the 

ISrTTTTTTTIT 



Figure 15 

number of lights used. If, for instance, only one light is used, 
there is a current of about one-half ampere, but if ten 16 
cp. lights are used there must be a current of about five 
amperes. Where many lights are used with this system, the 
main wires require to be quite large, and must always be 
proportional to the number of lights. This system is oper- 
ated usually at 110 volts and is suitable for residences, stores, 
factories and all indoor illumination. It is not well adapted 
to the transmission of light and power over long distances. 
The 3-wire system shown in Figure 16 combines many of 




rTTTTTXT 



^t t t H t t t 



^g 



Figure 16 



the advantages of both the foregoing systems. As will be 
seen from the diagram, it consists of two dynamos connected 
in series and a system of wiring of one positive +, one nega- 
tive — and a neutral = wire. So long as an equal number of 



34 



MODERN ELECTRICAL CONSTRUCTION. 



lights are burning on both sides of the neutral wire, this 
wire carries no current, but should more lights be in use 
on one side of the system than on the other, the neutral wire 
will be called upon to carry the difiference. If all the lights 
on one side are out, the dynamo on that side will be running 
idle. 

The currents in the neutral wire may be either positive 
or negative in direction. The principal advantage of this sys- 
tem is that with it double the voltage of the 2-wire systems 
is employed and yet the voltage at any lamp is no greater than 
with the use of two wires. It is customary to use 110 volts 
on each side of the neutral wire and this gives a total volt- 
age over the two outside wires of 220 volts. As the same 
current passes ordinarily through two lamps in series, we 
need, for a given number of lamps only half as much current 
as with 2-wire systems and can, therefore, vise smaller 
wires. For the same number of lights and the same per- 



6 



Figure 17 

centage of loss the amount of copper required in the two 
outside wires is only one-fourth that of 2-wire systems ; to 
this must be added a third wire of equal size for the neutral, 
so that the total amount of copper required with this system 
is ^ of that of 2-wire system using the same kind of lamps. 
Incandescent lamps are often run in multiple-series, as in 



WIRING SYSTEMS. 



35 



Figure 17, without a neutral wire. The number of lamps to 
be used in series depends upon the voltage of the dynamo. 
If that is 550, five 110 volt lamps are required in each group, 
Dr ten 55 volt lamps. 

If the filament of one lamp breaks all of the lamps in 



HHH 



^ ^^ ^ ^^ 



i-O- 

-o- 
-o- 
-o 
-o- 
o- 



Figure 18 

that group are extinguished and if one is to be used all must 
be used. 

Figure 18 shows the diagram of a series-multiple system. 
This style of wiring should be avoided. 

A diagram of an alternating current system is shown in 



W 





m 

Figure 19 

Figure 19. In this system extremely high voltage is used and 
consequently the currents are never very great. This makes 



36 MODERN ELECTRICAL CONSTRUCTION. 

it extremely useful for long distance transmission. Since, 
however, the high pressure employed cannot be used directly 
in our lamps it must be transformed into lower pressure. 
This is done by means of transformers, and it is possible to 
reduce the line voltage to any desirable extent. As the volt- 
age is reduced, however, the current increases and the wires 
taken from the transformers into the buildings must be as 
large as those for 2-wire systems using the same kind of 
lamps. The high pressure, or primary wires, are rarely 
allowed inside of buildings. 

The Transmission of Electrical Energy. 

We have seen that currents of electricity flow only in 
electrical conductors, and that these conductors are usually 
arranged in the form of wires. We have further seen that 
the power transmitted is proportional to the product of the 
volts and amperes used. The actual amount of energy trans- 
mitted being the product of the above multiplied by the time. 

Currents of electricity always encounter some resistance 
and in consequence of this resistance, generate heat; the 
generation of heat in any electric circuit being proportional 
to the square of the current multiplied by the resistance. 
This formula, P X R expresses the loss of electrical energy 
due to the resistance of the conductors and which reappears 
in the form of heat. If this loss is not kept within reasonable 
limits, the wires will become very hot and destroy the in- 
sulation or ignite surrounding inflammable material. The 
above loss and hazard is generally guarded against by insur- 
ance companies and inspection boards by designation of the 
current in amperes which certain wires may be allowed to 
carry. 

Table No. 1 gives the currents which the National Board 
of Fire Underwriters has decided to consider safe and which 



ELECTRICAL TRANSMISSION 37 

should be closely followed, and on no account should wires 
smaller than those indicated be used. There is no harm and 
no objection to using wires larger than indicated,' but neither 
is there much gained unless the run be a long one as we shall 
see further on. 

The table of carrying capacities shows a great discrepancy 
between the relative cross-section of large and small wires 
and the currents they are allowed to carry; thus a No. 0000 
wire has a cross-section about eight times as great as that of 
No. 6, yet is allowed to carry less than five times as much. 

This discrepancy arises from the different rate of heat 
radiation. The radiating surface or circumference of a small 
circle or wire is relatively to its cross-section much greater 
than that of a large circle, and other things being equal the 
ratio existing between the heat given to a body and its radiat- 
ing surface determine its temperature. 

We have seen before that the power (either for lights or 
motors) consists of two factors ; current and pressure, ex- 
pressed respectively as amperes and volts. We have also seen 
that the power (watts) equals the product of these two; 
hence it follows, that as we increase either one, we may de- 
crease the other, or conversely, as one is decreased the other 
must be increased in order to deliver a given amount of 
power. We further know that it is the current alone which 
heats the wires and that accordingly as our currents are large 
or small, the wires used to transmit them must be large or 
small. It is obvious, therefore, that we can save much on 
copper by using higher voltages, since, if we double the 
voltage, we shall need only one-half as much current and can, 
therefore, use a much smaller wire. As an example : Sup- 
pose we have power to transmit which at 110 volts requires 
90 amperes. This requires a No. 2 wire containing 66,370 
circular mils. Now, if we double the voltage, we shall need 
only 45 amperes; this much we are allowed to transmit over 



38 MODERN ELECTRICAL CONSTRUCTION. 

a No. 6 wire which has only 26,250 circular mils. We must 
not, however, increase our voltage without due precaution and 
consideration, for high voltage is dangerous to life and in- 
creases the fire hazard. It also increases the liability to 
leakage and requires better and more expensive insulation 
which in a small measure offsets the other advantages. The 
usual voltage employed at present varies from 110 to 220 
volts for indoor lighting and power; 500 to 650 volts for 
street railway work and from 2 to 20,000 volts for long 
distance transmission. The higher voltages mentioned are 
seldom brought into buildings, and are nearly always used 
with some transforming device which reduces the pressure to 
110 or 220 volts for indoor lighting or power. 

The flow of current through a given lamp, motor, or re- 
sistance determines the light, power or heat obtainable from 
such device. We know that the flow of current in turn 
(other things being equal) varies as the E. M. F. maintained 
at the terminals of any of these devices. Consequently in 
order to obtain a steady flow of current it is necessary to 
provide a steady E; M. F. 

The loss of E. M. F. in any wire is equal to the current 
flowing in that wire multiplied by the resistance of the wire. 
Since it is impossible to obtain wires without resistance, it 
is also impossible to establish a circuit without loss and 
wherever electricity is used some loss must be reckoned with. 
We may make this loss as large or as small as we desire. 
Where the cost of fuel is high, it is important to keep this 
loss quite small, using for that purpose larger wires. On the 
other hand where there is an abundance of cheap fuel, or, 
where, for instance, water power is used, it will be more 
economical to waste Ave or ten per cent of the electrical 
energy than to spend the money needed to provide the copper 
necessary to reduce the waste to one or two per cent. 

In this connection, however, it must not be overlooked that 



ELECTRICAL TRANSMISSION 39 

the quality of the service depends to a great extent upon the 
loss allowed and here the nature of the business supplied must 
be taken into consideration. In yards, warehouses, barns, 
etc, a variation of five or ten per cent in candle power may 
not matter much, but in residences or offices it is very 
annoying. 

The loss in voltage depends, as we have already seen, 
upon the current used, and the resistance of the wire em- 
ployed. If the current is decided upon, we can reduce the loss 
only by reducing the resistance; the resistance can be re- 
duced only by increasing the size of wire used. If we double 
the cross-section of the wire, we decrease the resistance one- 
half and consequently reduce the loss or variation in volt- 
age one-half. Thus it will be seen that as we attempt to 
reduce the loss in voltage to a minimum we shall require 
very large wires and thus greatly increase the cost of our 
installation. 

For instance, If a line be in operation with a loss -^f 
twenty per cent, by doubling the amount of copper, we reduce 
the loss to ten per cent. In order to reduce our loss to five 
per cent, we must again double the amount of copper; and 
to reduce the loss still more, say to lYz per cent, a wire 
of double the cross-section of the last must be used. If the 
cost of copper in the original installation utilizing eighty per 
cent of the energy be taken as 1, then the cost of copper to 
utilize ninety per cent will be 2; of ninety-five per cent, 4; 
and of ninety-seven and one-half per cent, 8; and no amount 
of copper will ever be able to save the full 100 per cent. 
We must not overlook, however, that although a reduction of 
loss from four to two per cent requires us to double the 
amount of copper, it does not necessarily double the cost of 
our installation, for in many cases it adds but a small per- 
centage to the total cost. For instance, if it were decided to 
use No. 12 instead of No. 14 wire in moulding or insulator 



40 MODERN ELECTRICAL CONSTRUCTION. 

work, the cost of labor would not be appreciably affected 
thereby; similarily m connection with a pole line, the dif- 
ference in total cost occasioned by the use of say No. 6 
instead of No. 10 wire would be small. 



Calculation of Wires. 

In electrical calculations so far as they relate to wiring, 
the circular mil plays an important part, and it becomes 
necessary to thoroughly understand its meaning. The mil 
is the 1/1000 part of an inch, consequently one square inch 
contains 1,000x1,000 equals 1,000,000 square mils. If all elec- 
trical conductors were made in rectangular form, we should 
be able to get along nicely by the use of the square mil, but, 
since they are nearly all in circular form, the use of the square 
mil as a unit would necessitate otherwise unnecessary figures. 
The circular mil means the cross-section of a circle one mil 
in diameter, whereas the square mil means a square each 
side of which is equal to one mil in length. Square mils, 
can, therefore, be transformed into circular mils by dividing 
by .7854, and circular mils into square mils by multiplying 
by .7854, since it is well known that a circle which can be 
inscribed within a square bears to that square the ratio of 
.7854 to 1. 

To illustrate : Using square mils if we wish to determine 
the cross-section of a wire having a diameter of 50 mils, we 
must first square the diameter and then multiply by .7854; 
50 X 50 X .7854, or 1963.5, which is the cross section of the 
wire expressed in square mils. To express the cross-section 
in circular mils, we have but to square the diameter, or 50 X 
50 =^ 2500 circular mils. The 2500 circular mils are exactly 
equal to the 1963.5 square mils. The adoption of the circular 
mil simply eliminates the figure .7854 from the calculations. 

The resistance of a copper wire having a cross-section of 



CALCULATION OF WIRES '*'' 

one mil and a length of one foot is from 10.7 to 10.8 ohms 
the variation being due to the temperature of the wire. 10.8 
ohms is the resistance usually taken. This resistance in- 
creases directly as the length and decreases as the cross-sec- 
tion increases. The resistance of any copper wire can, there- 
fore, be found by mukiplying its length by 10.8 and dividing 
by the number of circular mils it contains. Expressed m 
L X 10.8 

formula this becomes R = where L stands for the 

C. M. 
total length of wire in feet, and C. M. for the cross-section 
in circular mils, and R for the resistance in ohms. In 
order to find the loss in volts, we must multiply the resistance 
bv the current used. Representing this current by I, the 
I X L X 10.8 , ^ 

formula becomes - = V; V being the volts lost. 

C. M. 
It is, however, seldom necessary to find how many volts would 
be lost with a certain wire and current, but rather to find how 
many circular mils are necessary in a wire so that the volts lost 
may not exceed a certain percentage. In order to determine this, 
we transpose V and C. M. and the formula now becomes 

I X L X 10.8 ^ , ^ 11- 
^=C. M. This is the final formula and gives 

V 
directly the number of circular mils a wire must have so that 
the loss with this current and length of wire shall not exceed 
the limits set by V. 

As an example, we have a current of 20 amperes to trans- 
mit a distance of 200 feet and the loss shall not exceed 
two per cent; voltage 110. This requires 400 feet of wire 
(two wires 200 feet long) and two per cent of HO is 2.2. We 
therefore have 20 X 400 X 10.8 divided by 2.2, which gives 
us 39,270 circular mils, which we see by table I is a little less 
than a No. 4 wire. 



42 MODERN ELECTRICAL CONSTRUCTION. 

The above formula will answer for all 2-wire work^ 
whether it be lights or power. 

It is simply necessary to find the current required with 
whatever devices are to be used. 

These calculations are not often made in actual practice. 
It is much easier to refer to tables such as II. Ill, IV, V, VI, 
given at the end of this volume, by which the proper size 
of wire can be determined at a glance almost. 

In connection with 3-wire systems using two lamps in 
series, we need to calculate the two outside wires only, the 
neutral wire should then be taken of the same size. We must 
however assume double the voltage existing on either side 
of the neutral; that is to say, a 2-wire system using 110 volts 
would be figured at 110 volts, while a 3-wire system, using 
110 volt lamps on each side of the neutral wire would be 
figured at 220 volts. 

It must also be noted that with 3-wire systems the cur- 
rent required is only ^ of that required with 2-wire sys- 
tems. Ordinarily we have two larhps in series and the same 
current passes through both. Applying this to our formula 
we see that with the 3-wire system the current I is only half 
as great as with 2-wire systems and (the percentage of loss 
in both cases being the same) V, which stands for the volts 
to be lost, becomes twice as great. Owing to these two fac- 
tors, the wire for 3-wire systems need have only % as many 
circular mils as that of a 2-wire system with the same per- 
centage of loss. To this must be added the neutral wire so 
that the total cost of wire must be Y^ of that for the 2-wire 
systems. 

The amount of copper required in power transmission for 
a given percentage of loss varies as the square of the voltage 
employed. By doubling the voltage we can transmit power 
with the same loss four times as far; or, if we do not change 
distance or wire, we shall have only one-fourth of the loss 



CALCULATION OF WIRES 43 



we had before. A practical idea of the laws governing the 
distribution of circuits and the losses in voltage and wire 
which are unavoidable may be gained from Figure 20. 

Figure 20 shows 96 incandescent lights arranged on one 
floor ^and placed 10 feet apart each way. With all cutouts 
placed at A and circuits arranged as in No. 1, 2,080 feet of 
branch wiring for the eight circuits of 12 lights each, will be 
required. If the cutouts be placed in the center, B, the same 
length of wire will be necessary. We have in this case merely 
transferred the cross wires from one end of the hall to the 
center. If we arrange two sets of cutouts as at C and D 
and run circuits as 3 and 4 the total amount of wire necessary 
will be only 1,920 feet. By this arrangement we avoid the 
necessity of crossing the space indicated by dotted lines at 
the right, opposite B. 

If we run the circuits on the plan of No. 2, the least amount 
of wire for the eight circuits will be 2,560 ft. Such wir- 
ing would require extra wires feeding the various groups. 
Should we run a set of mains along ACBD, and make 12 
circuits of the installation by placing one cutout for each 
eight lights, the amount of wire required will be 1,680 feet. 
If we run a set of mains through B as shown by dotted lines 
using 12 lights per circuit, 1,760 feet of wire will be re- 
quired. If we now double the .number of lights in the same 
space or limit the number per circuit to six, we shall require 
3,200 feet of wire to feed them all from A, but only 2,400 to 
feed them from B; to feed them all from the two centers C 
and D will also require 2,400 feet. 

The most economical location of cutout centers will, with 
even distribution of light, and in regard to branch wiring 
only, be such that it is unnecessary to run circuits like No. 2; 
in other words, not more than the number of lights allowed on 
one circuit should lead away from it in one direction. 

Suppose, for instance, the number of lights be increased 



44 



MODERN ELECTRICAL CONSTRUCTION. 



c 



lb 



o " o 



o 



%b 



o 



•z 



• • 



Tl 



^W=^5 n — ^ Tf "f f 



o 



oxlirn 



O Q 

O 



( ) ( ■) =D 



() O ZX) 



OXI () () () 



IT 



O () 



X) p , o 



• o 
o o 



o o 



Figure 20 



CALCULATION OF WIRES 



45 



by one-half or (which amounts to the same thing in wire), 
the number of lights per circuit be limited to eight. If we 
run all branch circuits from A, we shall need a total of 2,760 
feet. It will require just as much wire to run the 64 lights 
below X as was required to run the whole 96 before ; viz. : 
2080 feet; to this must be added the wire necessary to run the 
four circuits above which is 680 feet. By extending our 
mains to the point X, we car save eight runs of wire each 
equal in length to the distance 'between A and X. X is the 
point of extreme economy as regards branch wires and nothing 
can be gained in this respect by extending the mams any 
further unless several cutout centers are decided upon as 
before explained. Whether it be more economical to extend 
the mains to X, or run branch circuits from A, depends upon 
the relative cost, in this instance, of 30 feet of mains and 
480 feet of branch wires. 

With an uneven distribution of lights as indicated by the 
black circles, each of which may be taken as an arc lamp or 
cluster of incandescent lamps, the most economical location 
of cutouts will be at Z. To move them farther to the right 
would shorten the wires of five circuits and lengthen them on 
eight; to move either up or down in the group of eight would 
also lenghten more wires than it would shorten. 

In laying out circuits for electric lights, however, we 
must not take into consideration the cost of wire only. In 
many cases the loss in voltage is of far greater importance, 
not only because it means a steady waste of power, but also 
because of unsatisfactory illumination, lamps in different 
parts of a circuit not being of the same candle power, or 
the light in one place varying greatly when lights in another 
place are turned on or off. 

Some idea of the variation in voltage in different parts 
of differently arranged circuits can be obtained from Figure 20. 
The length of wire in circuit 1 is 35 feet to the first lamp and 



46 MODERN ELECTRICAL CONSTRUCTION. 

10 feet from this to the next, etc. The voltage at the cut- 
out A is 110 and at each lamp is given the actual voltage 
existing at that point with all lamps burning. The wire of 
the circuit is No. 14 and with 55 watt lamps, the loss to the 
last lamp over a run of 145 feet is a trifle over two and one- 
half per cent when all lamps are burning. 

Circuit No. 2 is figured as of the same length as No. 1, 
and supplies the same number of lamps, but at a much greater 
loss, slightly over four per cent to the last lamp. Circuits 3 
and 4 feeding from C contain equal lengths of wire, but 
there is quite a difference in loss ; in 3 only .75 of one volt, 
while in 4 it is a little over two volts. From study of Figure 
20 we may learn that the arrangement of circuit 1 is fairly 
satisfactory especially if the nature of the work done under 
it is such that only part of the lamps are used at the same 
time. Circuit No. 2 is bad if all lights are used at once, and 
it should be wired with No. 10 or 12 wire. Whenever the loca- 
tion of lights is such as to allow a circuit like No. 3 to be run, 
the loss can be kept very low with a minimum of wire. In 
general the more cutout centers there are established in propor- 
tion to the number of lights, if mains are properly arranged, 
the less will be the loss in pressure and the more satisfactory 
the service. 



NOTICE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class A. 

STATIONS AND DYNAMO ROOMS. 

Includes Central Stations, Dynamo, Motor and Storage- 
Battery Rooms, Transformer Substations, Etc. 

1. Generators. 

a. Must be located in a dry place. 

Perfect insulation in electrical apparatus requires that the 
material used for insulation be kept dry. While in the con- 
struction of generators the greatest care is taken, so that al) 
current carrying parts are well insulated, still, if moisture is 
allowed to settle on the insulation, trouble is almost sure to 
occur. For this reason a generator should never be installed 
where it will be exposed to steam or damp air, or in any place, 
where through accident, water may be thrown against it. 

b. Must never be placed in a room where any hazardous 
process is carried on, nor in places where they would be ex- 
posed to inflammable gases or flyings of combustible materials. 

In even the best constructed dynamos there is always more 
or less sparking at the brushes and small pieces of hot carbon 
are sometimes thrown off. As a general rule in buildings 
where there is considerable dust, such as in wood-working 
plants, grain elevators and the like, the dynamo is located in 
the engine room, which is generally isolated from the dusty 
part of the building. 

c. Must be thoroughly insulated from the ground wherever 
feasible. Wooden base-frames used for this purpose, and 



48 



MODERN ELECTRICAL CONSTRUCTION. 



wooden floors which are depended upon for insulation where, 
for any reason, it is necessary to omit the base-frames, must 
be kept filled to prevent absorption of moisture, and must be 
kept clean and dry. 

Where frame insulation is impracticable, the Inspection 
Department having jurisdiction ma}'-, in writing, permit its 
omission, in which case the frame must be permanently and 
effectively grounded. 

A high-potential machine, which on account of great weight 
or for other reasons, cannot have its frame insulated from the 
ground, should be surrounded with an insulated platform. 
This may be made of wood, mounted on insulating supports, 
and so arranged that a man must always stand upon it in order 
to touch any part of the machine. 

In case of a machine having an insulated frame, if there is 
trouble from static electricity due to belt friction, it should 
be overcome by placing near the belt a metallic comb connected 
with the earth, or by grounding the frame through a very 
high resistance of not less than 300,000 ohms. 

The smaller generators are usually insulated on wooden 
base frames. A base frame suitable for this work is shown in 




Figure 21 



Figure 22 



Figure 21. Almost any kind of wood, well varnished, is very 
good for this purpose. The base frame is screwed to the floor or 
foundation and the slide rail (which is used where the dy- 
namo is belted to the engine to allow the tightening and slack- 



GENERATORS 



49 



ening of the belt) is independently attached to it, that is, 
the same bolt must not be used to hold the slide rail to the 
base frame and the base frame to the floor, as this would be 
liable to ground the frame. The direct connected machines 
(dynamo and engine on same bed plate) are often insulated 
by the use of mica washers and bushings surrounding the 
bolts which fasten the dynamo to the bed plate and by using 
an insulated flange coupling between the shaft of the dynamo 
and that of the engine. Figure 22 shows a section of a flange 
coupling insulated in this way, the heavily shaded parts rep- 
resenting the insulating material. 

The larger machines, which on account of their weight 
cannot be insulated, must be permanently and effectually 
grounded. Where the engine and dynamo are direct con- 
nected a very good ground is obtained through the engine con- 
nections. Where belts are used a good ground can be ob- 
tained by fastening a copper wire under one of the bolts on the 
dynamo and connecting the other end of the wire to available 




Figure 23 

water pipes. In the case of high tension machines, especially 
series arc, the machine should always be surrounded by an 
insulated platform so arranged that a man must stand on it in 
order to touch any part of the machine either live parts or 



50 MODERN ELECTRICAL CONSTRUCTION. 

frame and in handling such a machine only one hand at a time 
should be used. A hardwood platform mounted on insulators 
will serve very well for this purpose or suitable platform_s may 
be obtained from dealers in electrical supplies. 

Figure 23 shows a metallic comb such as is occasionally 
used to overcome the static electricity due to the friction of 
the belt. A strip of metal, one end of which is cut with a 
number of projecting points, is suspended crosswise a short 
distance above the belt. A wire connects this plate to any 
suitable ground. 

A resistance for grounding the generator frame in accord- 
ance with this rule is constructed of ground glass equipped 
with two metal terminals separated a short distance and con- 
nected by means of a lead pencil mark. One terminal is con- 
nected to the frame of the machine and the other to the ground. 

d. Every constant-potential generator must be protected 
from excessive current by a safety fuse, or equivalent device 
of approved design in each lead wire. 

These devices should be placed on the machine or as near 
it as possible. 

Where the needs of the service make these devices imprac- 
ticable, the Inspection Department having jurisdiction may, in 
writing-, modify the requirements. 

The fuses required by this rule are often mounted on the 
dynamo, but the general practice at the present time is to 
mount all fuses on the switchboard. A fuse should be placed 
in each lead ; that is, each of the main wires from the dynamo 
should be protected by a fuse. A fuse should never be placed 
in the field circuit wire. Where two or more dynamos are 
run in parallel the equalizer connection (a wire connecting all 
the armature terminals from which the series fields are taken 
and which tends to equalize the load between the various ma- 
chines) is sometimes carried through a 3-pole switch on the 
switchboard and is often fused. It is immaterial whether this 
equalizer is fused or not, as fusing it adds no protection. If it 



GENERATORS Si 

is fused the fuse should be at least the same size as used in 
the leads. 

Circuit breakers are very often used for the protection in 
the dynamo leads. They are generally mounted on the switch- 
board and connected in the circuit ahead of the main switch. 
As a general rule circuit breakers are not approved unless 
fuses are also installed in the circuit. The circuit-breaker as 
at present constructed is in nearly all cases a much more 
efficient and reliable device than the fuse, and its use is to be 
recommended. Single-pole circuit breakers are approved if fuses 
are also used. As to the relative currents at which the fuse 
and circuit breaker should be set to operate, authorities differ. 
Some advise both to be set to operate at the same current 
strength, so that the fuse, which takes a longer time to operate, 
will blow only in case the circuit breaker fails. Another recom- 
mends the fuses to be of such capacity as to carry any load 
which will be required of them and to set the circuit breaker 
a little higher than the fuses, so that the fuses will operate 
on overload and the circuit breaker on short circuit. 

The practice of setting the fuses at about twenty-five per 
cent, above the circuit breaker seems to be preferred, for it 
occasionally happens when both are set to operate at the same 
current, the fuse alone will "blow," due to the excessive heat 
produced in the fuse at full load. 

Cases are sometimes found where the cessation of current 
due to the blowing of a fuse could cause more damage than 
would result from an overload, as, for instance, where the 
dynamo operates some safety device. In cases of this kind the 
Inspection Department having jurisdiction may modify the 
requirements. 

e. Must each be provided with a waterproof cover. 

/. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the nor- 
mal speed in revolutions per minute. 



52 MODERN ELECTRICAL CONSTRUCTION. 

2. Conductors. 

From generators to switchboards, rheostats or other instru- 
ments, and thence to outside hnes. 

a. Must be in plain sight or readily accessible. 

b. Must have an approved insulating covering as called for 
by rules in Class "C" for similar work, except that in central 
stations, on exposed circuits, the wire which is used must have 
a heavy braided, non-combustible outer covering. 

Bus bars may be made of bare metal. 

Rubber and "weatherproof" insulations ignite easily and 
burn freely. Where a number of wires are brought close to- 
gether, as is generally the case in dynamo rooms, especially 
about the switchboard, it is therefore necessary to surround 
this inflammable material with a tight, non-combustible outer 
cover. If this is not done, a fire once started at this point 
would spread rapidly along the wires, producing intense heat 
and a dense smoke. Where the wires have such a covering 
and are well insulated and supported, using only non-com- 
bustible materials, it is believed that no appreciable fire 
hazard exists, even with a large group of wires. 

c. Must be kept so rigidly in place that they cannot come 
in contact. 

d. Must in all other respects be installed with the same 
precautions as required by rules in Class "C" for wires carry- 
ing a current of the same volume and potential. 

In wiring switchboards, the ground detector, volt meter 
and pilot lights must be connected to a circuit of not less than 
No. 14 B. & S. gage wire that is protected by a standard fuse 
block; this circuit is not to carry over 660 watts. 

A number of different methods are used for running wires 
in dynamo rooms. Where the dyanmo is located in a room 
with a low ceiling, or where it is not desirable to run the 
wires open, metal conduits may be imbedded in the floor and 
the wires run in them. If the engine room is located in the 
basement or in any place where water or moisture is liable 
to gather in the conduits the wires should be lead covered. 
At outlets the conduits should be carried some distance above 
the floor level and close to the frame of the machine, where 
they will be protected from mechanical injury. If the space 
under the machine will allow it, the conduit should be ended 



SWITCHBOARDS S3 

there where it will be protected by the base frame. Where 
lead covered wires are used, the lead should be cut back some 
distance from the exposed part of the wire and the end of the 
lead should be well taped and compounded so that no 
moisture can creep in between the lead and the insulation. 

In place of the metal conduits tile ducts can be used ; or, 
if the floor is of cement, a channel may be left in the floor 
and the wires run in it. A removable iron cover should be 
provided. 

The wires may be run open on knobs or cleats as described 
in Class C. Where there are many wires, cable racks, con- 
structed of wood or preferably iron, having cleats bolted to 
them, may be used. As a general rule moulding should not 
be used for this class of work. Especially in central stations 
the generators are often called upon for a very heavy overload 
and should the wires become overheated a fire is much more 
apt to result than if the mains were run open where any 
trouble could be immediately noticed. 

3. Switchboards. 

a. Must be so placed as to reduce to a minimum the 
danger of communicating fire to adjacent combustible material. 

Special attention is called to the fact that switchboards 
should not be built down to the floor, nor up to the ceiling-. 
A space of at least 10 or 12 inches should be left between the 
floor and the board, and 3 feet, if possible, between the ceiling 
and the board, in order to prevent fire from communicating 
from the switchboard to the floor or ceiling, and also to pre- 
vent the forming of a partially concealed space very liable to 
be used for storage of rubbish and oily waste. 

h. Must be made of non-combustible material or of hard- 
wood in skeleton form, filled to prevent absorption of moisture. 

If wood is used all wires and all current-carrying parts of 
the apparatus on the switchboard must be separated therefrom 
by non-combustible, non-absorptive insulating material. 

c. Must be accessible from all sides when the connections 
are on the back, but may be placed against a brick or stone 
wall when the wiring is entirely on the face. 



54 



MODERN ELECTRICAL CONSTRUCTION. 



If the wiring is on the back, there should be a clear space 
of at least 18 inches between the wall and the apparatus on 
the board, and even if tlie wiring- is entirely on the face, it is 
much better to have the board set out from the wall. The 
space back of the board sliould not be closed in, except by 
grating- or netting either at the sides, top or bottom, as such 
an enclosure is almost sure to be used as a closet for clothing 
or for the storage of oil cans, rubbish, etc. An open space is 
much more likely to be kept clean, and is more convenient for 
making repairs, examinations, etc. 

d. Must be kept free from moisture. 

e. On switchboards the distances between bare live parts 




Figure 24 



of opposite polarity must be made as great as practicable, and 
must not be less than those given for tablet-boards (see No. 
53 A). 

The switchboard may be located in any suitable place in the 



RESISTANCE BOXES 55 

dynamo room. It should generally be placed in a central 
position as close as possible, without inconvenience, to all 
machines and perfectly accessible. Do not locate a switchboard 
under or near a steam or water pipe or too close to windows, 
as these may accidentally be the means of wetting the board. 

The material generally used for the construction of switch- 
boards is slate or marble, free from metallic veins. If metallic 
veins are not guarded against they may cause great leakage of 
current, which will manifest itself in heating the slate or 
marble. 

The switchboard may be made of hardwood in skeleton 
form (see Figure 24), but in this case all switches, cutouts, 
instruments, etc., must be mounted on non-combustible, non- 
absorptive insulating bases, such as slate or marble and all 
wires must be properly bushed where they pass through the 
woodwork and must be supported on cleats or knobs. Wood 
base instruments are not approved. 

Marble or slate boards are usually set in angle iron frames 
and are much safer and better than the skeleton board shown. 
It is a good plan to have the iron legs rest on a wooden base, 
so that they will be insulated from the ground. 

Although only 18 inches clear space is required back of 
the board, where the board is back connected, this should be 
increased wherever possible, especially in the case of large 
boards. 

4. Resistance Boxes and Equalizers. 

(For construction rules, see No. 6o.) 

a. Must be placed on a switchboard or, if not thereon, 
at a distance of at least a foot from combustible material, or 
separated therefrom by a non-inflammable, non-absorptive, 
insulating material such as slate or marble. 

The attachments of the separating- material to its support 
and to the device must be independent of each other, and the 
separating- material must be continuous between the device and 
the support; that is, the use of porcelan knobs will not be 
accepted. 




56 MODERN ELECTRICAL CONSTRUCTION. 

Ordinarily the dynamo field rheostat is mounted on the 
back of the board if the board is back connected, a small hand 
wheel being provided so that 
the rheostat may be operated 
from the front of the board. 
If the switchboard is in skele- 
ton form, or if the rheostat is 
placed on a wall, it should be 
mounted on a solid piece of 
slate or marble. Separate 

screws should be used for at- ' jp^^ 25. 

taching the rheostat to the slate 

or marble and the slate or marble to the wall, for, if the same 
screws were used for this purpose, they would be apt to ground 
the rheostat frame. (See Figure 25.) 

On central stations where current is furnished over a large 
area, there is on some of the circuits, especially the long ones, 
a considerable ''drop," or loss of potential. In order to keep 
the voltage at the point of supply on these circuits at the 
proper value, the voltage at the station must be raised. This 
in turn causes the voltage on those circuits near the dynamo 
to become excessive. Equalizers, which are large resistance 
boxes generally constructed of iron wire or strips, and capable 
of carrying a heavy current, are connected in the circuits and 
adjusted at such resistances as to make the voltage at the 
various points of supply uniform. They are generally too 
heavy to mount on the board, but should be raised on non- 
combustible, non-absorptive, insulating supports and should 
be separated from all inflammable material. 

b. Where protective resistances are necessary In connec- 
tion with automatic rheostats, incandescent lamps may be 
used, provided that they do not carry or control the main 
current or constitute the regulating resistance of the device. 

When so used, lamps must be mounted in porcelain recep- 



LIGHTNING ARRESTORS 57 

tacles upon non-combustible supports, and must be so arranged 
that the}^ cannot have impressed upon them a voltage greater 
than that for which they are rated. They must in all cases be 
provided with a name-plate, which shall be permanently at- 
tached beside the porcelain receptacle or receptacles and 
stamped with the candle-power and voltage of the lamp or 
lamps to be used in each receptacle. 

5. Lightning Arresters. 

( For construction rules, see No. 63.) 

a.. Must be attached to each wire of every overhead cir- 
cuit connected with the station. 

It is recommended to all electric light and power companies 
that arresters be connected at intervals over systems in such 
numbers and so located as to prevent ordinary discharges en- 
tering (over the wires) buildings connected to the lines. 

b. Must be located in readily accessible places away from 
combustible materials, and as near as practicable to the point 
where the wires enter the building. 

Station arresters should generally be placed in plain sight 
on the switchboard. 

In all cases, kinks, coils and sharp bends in the wires be- 
tween the arresters and the outdoor lines must be avoided as 
far as possible. 

c. Must be connected with a thoroughly good and perma- 
nent ground connection by metallic strips or wires having a 
conductivity not less than that of a No. 6 B. & S. gage copper 
wire, which must be run as nearly in a straight line as possible 
from the arresters to the ground connection. 

Ground wires for lightning arresters must not be attached 
to gas pipes within the buildings. 

It is often desirable to introduce a choke coil in circuit 
between the arresters and the dynamo. In no case should the 
ground wires from the lightning arresters be put into iron 
pipes, as these would tend to impede the discharge. 

A lightning discharge is simply a discharge of electricity at 



Gro^ 



58 MODERN ELECTRICAL CONSTRUCTION. 

very high potential. While the insulation of the ordinary wire 
serves very well for the voltages 
for which it is used it offers very 
little resistance to a current of 
such high potential, and providing 
the discharge can reach the ground 
\AAAAAAAAA/\/-/y^y ^^ jumping through the insula- 
/VWWWWWWX ^^o^^' '^^ will generally take that 
course unless some easier path is 
offered to it. A lightning arrester 

in its simplest form consists of 

Fig. 26. two metal plates separated by a 

small air space as shown in Fig- 
ure 26. One of the plates is con- 
nected to the line and the other to the ground, a set being pro- 
vided for each line wire to be protected. 

The air space between the metal plates offers a much lower 
resistance to the passage of such a sudden current as a dis- 
charge of lightning consists of, than do the magnets of a 
dynamo, for instance, or highly insulated parts of the line. 
The current, therefore, jumps the air space and passes to 
ground. When the current jumps this air space it produces 
an arc similar to that seen in an arc lamp, and after the light- 
ning discharge is over the dynamo current is very likely to 
maintain this arc and thus cause a short circuit from one 
lightning arrester through the ground to the other. Different 
methods of preventing this by interrupting the arc have been 
devised. 

Figure 27 shows the T. H. lightning arrester, in which 
the arc is extinguished by a magnetic field set up by the electro- 
magnet. In the Wurts non-arcing lightning arrester (Figure 
28) the discharge takes place across the air gaps between the 
cylinders ; these are made of a metal which will not arc. 

A choke coil is essentially an electro-magnet, and like all 



TESTING 



59 



magnets offers a very high resistance to a sudden rise in cur- 
rent strength, and is, therefore, an additional protection to 
other magnets in the circuit. 

6. Care and Attendance. 

a. A competent man must be kept on duty where gen- 
erators are operating. 




Figure 27 

b. Oily waste must be kept in approved metal cans and 
removed daily. 

Approved waste cans shall be made of metal, with legs 
raising can 3 inches from the floor and with self-closing 
covers. 



7. Testing of Insulation Resistance. 

a. All circuits except such as are permanently grounded 
in accordance with Rule 13 A must be provided with reliable 
ground detectors. Detectors which indicate continuously and 



60 



MODERN ELECTRICAL CONSTRUCTION. 



give an instant and permanent indication of a ground are 
preferable. Ground wires from detectors must not be at- 
tached to gas pipes within the building. 

b. Where continuously indicating detectors are not feasible 
the circuits should be tested at least once per day, and prefer- 
ably oftener. 

c. Data obtanied from all tests must be preserved for ex- 



^ 



rrXi 



Ji w m n a 



H 




11 — m — IT 



® t "8 



"III n DT 



Qtound 



Figure. 28 



ammation by the Inspection Department having jurisdiction. 

These rules on testing to be applied to such places as may 
be designated by the Inspection Department having- jurisdic- 
tion. 

The exceptions to this rule are 3-wire direct current sys- 
tems where the neutral is grounded and 2 and 3-wire alter- 
nating current secondaries where the neutral or one side is 
grounded. 



TESTING 61 

In every installation of electric wiring there is a certain 
"leak" of current. This leak is partly between the wires and 
the ground and between the wires themselves. The amount of 
leak varies, but is always dependent on the insulation resist- 
ance. Where a small amount of wire is well installed the leak 
should be very small, but in the case of large installations 
or where the wiring has been poorly done the flow of current 
to ground or between the wires of opposite polarity may be- 
come quite large. Wires lying on pipes or on damp wood- 
work, crossed wires or live parts of apparatus mounted on 
wooden blocks, all tend to cut down the insulation resistance 
and increase the leak. The efifects of poor insulation are : First, 
it represents a useless loss of current, and, second, and more 
important, it means a possible cause of fire. 

The simplest way to determine the insulation resistance of 
a circuit is by means of a voltmeter. In Figure 29 if a volt- 
meter of known resistance is connected between one side of 
the circuit and the ground and there is a ground on the other 
side of the circuit, say at X, current will flow from the positive 
wire through the voltmeter then through the ground at X to 
the negative side of the circuit. The voltmeter needle will 
indicate a certain reading which we will call V\ If the volt- 
meter is now connected directly across the circuit we get the 
circuit voltage, which we will call V. The two readings, V^ 
and V, are to each other as the resistance of the voltmeter 
is to the combined resistance of the voltmeter and the ground 
at X ; or, calling the resistance of the voltmeter R and the resist- 

VI R V - VI 

ance of the ground at X r, we get — = , or r = R . 

V R + r VI 

As an example: On a certain system the voltage across the 
mains is 110, while with the voltmeter connected as shown in 
Figure 29 we obtain a reading of 30. The resistance of the 
voltmeter is 10,500 ohms. Supplying the numbers in the for- 



62 



MODERN ELECTRICAL CONSTRUCTION. 



110-30 

mula, r = 10,500 X = 28,000 ohms as the resistance to 

30 
ground of the negative side of the system. If the voltmeter is 



TTT 



Figure 29 Figure 30 

connected to ground from the other side, or — main, the resist- 
ance to ground of the + side can be obtained. 

If both sides of the system are grounded as at x and y, 
Figure 30 the voltmeter will be robbed of part of the current 
which would pass through it if Y were not in parallel with it. 
It will therefore not indicate correctly under such circum- 
stances. 

If, however, tests are frequently made and defects cleared 
up at once when noticed, it will seldom happen that two 
grounds occur on the system at the 
same time. An engineer or dynamo 
tender will soon learn what the in- 
sulation resistance of the plant in his 
charge should be and be governed ac- 
cordingly. 

A diagram of a direct current 
ground detector switch is shown in 
Figure 31. By throwing switch A 
down the — bus bar is connected to 
the ground through the voltmeter 
and by throwing switch B the + bar 
is connected to ground through the 
voltmeter. The ground wire should + 
be run to a water or steam pipe Fig:. 31. 




MOTORS 63 

(never to a gas pipe) or to some grounded part of the 
building. If no good ground is obtainable one may be 
made as described under 13 A. 

8. Motors. 

a. Must be thoroughly insulated from the ground wherever 
feasible. Wooden base-frames used for this purpose, and 
wooden floors which are depended upon for insulation where, 
for any reason, it is necessary to omit the base-frames, must 
be kept filled to prevent absorption of moisture, and must be 
kept clean and dry. 

Where frame insulation is impracticable, the Inspection 
Department having jurisdiction may, in writing, permit its 
omission, in which case the frame must be permanently and 
effectively grounded. 

A high-potential machine which, on account of great weight 
or for other reasons, cannot have its frame insulated, should 
be surrounded with an insulated platform. This may be made 
of wood, mounted on insulating supports and so arranged that 
a man must stand upon it in order to touch any part of the 
machine. 

In case of a machine having an insulated frame, if there is 
trouble from static electricity due to belt friction, it should be 
overcome by placing near the belt a metallic comb connected 
to the earth, or by grounding the frame through a very high 
resistance of not less than 300,000 ohms. 

Where motors with grounded frames are operated on sys- 
tems where one side is either purposely or accidentally 
grounded there exists a certain difference of potential be- 
tween the windings and the motor frame ; this difference of 
potential depending on the part of the circuit considered. At 
some places in the winding it will be the full difference of po- 
tential at which the motor is operating and at other points 
practically nothing. Should the conductors accidentally come 
in contact or "ground" on the motor frame a short circuit 
would result, as the circuit would then be completed through 
the motor frame and ground. To obviate this the motor frame 
should be insulated from the ground. This may be done either 
by setting the motor on a wood floor or by the use of a base 



64 MODERN ELECTRICAL CONSTRUCTION. 

frame, as with generators. A base frame should always be 
used where possible, for when a motor is set directly on the 
floor it is often impossible to keep the space under it clean, and 
there is always a liability of the floor being damp or of nails 
in the floor passing through the woodwork into some grounded 
part of the building or metal piping. A properly constructed 
base frame will allow of easy cleaning of the space under the 
motor. 

In the case of elevator or other motors where the shunt 
field is suddenly broken, a momentarily high voltage is induced 
in the field windings. If the frame of the motor is grounded 
this high voltage has a strong tendency to jump through the 
insulation of the wires to the metal work of the motor thus 
grounding the circuit. 

h. Must be wired with the same precautions as required 
by rules in Class "C" for wires carrying a current of the same 
volume and potential. 

Circuits for motors may be run in any of the ways described 
in Class "C" ; either open on knobs or cleats, in moulding, 
concealed knob and tube work or in conduit; or any combina- 
tion of these may be used. The conditions in each case will de- 
termine which is the best method to use. Where motors are 
placed some little distance from their switches and starting 
boxes, as in printing press work, conduit is often used for 
the wiring between the switch and starting box and the motor. 
This method provides very good mechanical protection for the 
wires and affords a safe >vay of running them. 

The motor leads or branch circuits must be designed to 
carry a current at least twenty-five per cent, greater than that 
for which the motor is rated, in order to provide for the in- 
evitable occasional overloading of the motor, and the increased 
current required in starting, without over-fusing the wires. 

The use of voltages above 550 is rarely advisable or necc^?- 
sary, and will only be approved when every possible safeguard 
has been provided. Plans for such installations should be sub- 
mitted to the Inspection Department having jurisdiction before 
any work on them is begun. 



^ 



MOTORS 65 

Good values to use for calculating the size of wire for 
branch conductors are given below. The question of loss of 
voltage is not taken into consideration here. 

110 volts 9.3 amperes per horsepower 

220 volts 4.6 amperes per horsepower 

500 volts 2 amperes per horsepower 

For mains supplying many motors it is not necessary to 
provide the twenty-five per cent, overload capacity, because it 
is not likely that all motors will start at the same time. If, 
however, any one motor has more than half the capacity of 
the whole installation, it is advisable to provide the overload 
capacity. For instance, if two motors, each of 50 amperes 
capacity, are fed over a line of 100 amperes capacity and 
one is started while the other is working at full load, they will 
overload that line twelve and one-half per cent. 

For mains supplying many small motors the size should 
be chosen for the total load connected, using the following 
values : 

110 volts 7.5 amperes per horsepower 

220 volts 3.75 amperes per horsepower 

500 volts 1.65 amperes per horsepower 

Where there are a number of 110-volt motors installed on 
the Edison 3-wire system, providing the load is evenly balanced 
between the two sides, the mains may be figured as though 
the motors were operating at 220 volts. The reason for this 
v/ill be easily seen when it is remernbered that two 110-volt 
motors operating in series on 220 volts (as they do on the 
Edison 3-wire system) take only one-half the current they 
would if operated on a straight 2-wire 110-volt system. 

c. Each motor and resistance box must be protected by a 
cut-out and controlled by a switch (see No. 17 a), said switch 
plainly indicating whether "on" or "off." With motors of one- 
fourth horsepower or less, on circuits where the voltage does 



66 



MODERN ELECTRICAL CONSTRUCTION. 



not exceed 300, No. 21 d must be complied with, and single 
pole switches may be used as allowed in No. 22 c. The switch 
and rheostat must be located within sight of the motor, except 
in cases where special permission to locate them elsewhere is 
given, in writing, by the Inspection Department having juris- 
diction. 

Where the crcuit-breaking device on the motor-starting 
rheostat disconnects all wires of the circuit, the switch called 
for in this section may be omitted. 

Overload-release devices on motor-starting rheostats will 
not be considered to take the place of the cut-out required by 
this section if they are inoperative during the starting of the 
motor. 

The switch is necessary for entirely disconnecting the motor 
when not in use. and the cut-out to protect the motor from 
excessive currents due to accidents or careless handling when 
starting. An automatic circuit-breaker, disconnecting all wires 
of the circuit may, however, serve as both switch and cut-out. 

For the larger size motors a cut-out must be installed for 
each motor, but with motors of ^ horsepower or less, where 




Li-ure 32 



the voltage does not exceed 300, a cut-out need be installed 
for every 660 watts only. This allows about 51/8 horsepower, 
motors, 3 1 /6 horsepower motors or 2 >4 horsepower motors 



MOTORS 67 

on one cut-out. Every motor, whether large or small must 
be controlled by a switch which will indicate whether the cur- 
rent is on or off. This is required to reduce the liability of a 
motor being accidentally left in circuit, which might result in 
serious trouble. Figure 32 shows a complete motor installa- 
tion as usually arranged. 

As a general rule fused knife switches are used for the 
larger motors, while with the smaller motors cut-out blocks 
and indicating snap switches are often used. If the motor is 
^ horsepower or less, and operated on a circuit where the 
voltage does not exceed 300, a single pole switch may be used. 
For all motors over ^ horsepower, and for all motors operated 
on voltages over 300, double pole switches must be used. The 
object of locating the switch and starting box within sight 
of the motor is that, should any trouble occur when the motor 
is being started, such as a short circuit or overload, it will 
be immediately noticed and the current shut off. If the con- 
ditions are such that it is necessary to locate the motor out 
of sight of the switch and starting box the motor should be 
located in a safe place, away from inflammable material. A 
special permit should be obtained from the inspection depart- 
ment having jurisdiction in order that the exact conditions may 
be noted. 

d. Must have their rheostats or starting boxes located so 
as to conform to the requirements of No. 4. 

The use of circuit breakers with motors is recommended, 
and may be required by the Inspection Department having 
jurisdiction. 

To be safe a rheostat should have as great a carrying ca- 
pacity as the motor itself, or else the arm should have a strong 
spring-throw attachment, so arranged that it cannot remain 
at any intermediate position unless purposely held there. 
Specifications governing the construction of rheostats are given 
in No. 60. 

Starting rheostats and auto-starters should be treated about 
the same as knife-switches, and in all wet, dusty or linty places 
should be enclosed in dust-tight, fireproof cabinets. If a special 
motor room is provided, the starting apparatus and safety de- 
vices should be included within it. Where there is any liability 



68 MODERN ELECTRICAL CONSTRUCTION. 

of short circuit across their exposed live parts being caused by- 
accidental contacts, they should either be enclosed in cabinets, 
or else a railing should be erected around them to keep un- 
authorized persons away from their immediate vicinity. 

In some cities the local rules allow the starting box or 
rheostat to be mounted on asbestos board, in which case it 
must be mounted out from the wall on porcelain knobs so that 
there will be at least one inch air space between the wall 
and the current-carrying parts. If the starting box or rheostat 
is to be mounted on a wall or other support where the frame 
would be grounded, it may be attached to a wood support and 
the wood support then independently attached to the wall. 
The best construction is to use slate or marble. If slate or 
marble is used it must be a continuous piece which will entirely 
cover the space back of the rheostat and the frame of the 
rheostat should be screwed to the slate or marble and the 
slate or marble then independently screwed to the wall, never 
using the same screw for attaching both. 

A starting box is a device for limiting the current strength 
during the starting of the motor by inserting a resistance in 
series with the armature. The ohmic resistance of the arma- 
ture of a shunt or compound v/ound motor is ordinarily very 
small. When such a motor is at rest and the current thrown 
directly on, the full voltage is thrown across the small resist- 
ance of the armature. Consider for a moment the case of a 
1 horespower 110 volt motor having an armature resistance of 
say 2 ohms, and taking, when running normally, 8 ampere?. 
Suppose the current were thrown on without the use of a 
starting box. According to Ohm's law the current through 
the armature would be 110/2=: 55 amperes. The results, were 
55 amperes sent through the armature, can easily be imagined. 
Now, suppose a resistance of 8 ohms were inserted in series 
with the armature when starting. In this case 110/10=: 11 
amperes only would have to pass through the armature and 
this the armature can easily stand. As the motor begins to 



MOTORS 



69 



revolve a counter electro-motive force is generated which op- 
poses the inrush of current. This counter electro-motive force 
increases until the motor reaches full speed and takes its nor- 
mal current. 

In the example given above at the first step of the starting, 
box there will be a current of 11 amperes flowing through a 
resistance of 8 ohms and the power consumed will be equal 
to 1- R, or 968 watts, which are lost in heat produced 
in the resistance wire. As this amounts to more than one 
horsepower thrown oJff in heat the advisability of mounting 
the rheostat away from inflammable material and of properly 
ventilating it can readily be seen. 

Figure 33 shows an illustration of an automatic starting 
box, and a diagram of the connections to a motor circuit. It 




" — WVWWH 



o 



Figure 33 



will be seen that the resistance coils are in series with the 
armature circuit. As the arm A is moved to the right, resist- 
ance is gradually cut out of the armature circuit until the 
arm reaches the last point, where it is automatically held in 



70 



MODERN ELECTRICAL CONSTRUCTION. 



position by means of the small magnet M, which is connected 
in series with the held circuit. By tracing out the circuits it 
will be found that the field connection is made on the first 
point of the rheostat, so that when the arm A is in the "oflf" 
position there is no current passing through the field coils. 




Figure 34 



It will also be noticed that the last contact upon which the 
arm rests when "off" is dead. If the supply current for any 
reason fails, current will cease to flow around the coils of the 
magnet M and it will become demagnetized, thus allowing 
the arm A to fly back to the "of¥" position. This overcomes 
the possibility of the main current being momentarily shut off 
and then thrown on when all the resistance is out of the arma- 
ture circuit. This device is known as "no-voltage" release. 

Another device known as the "overload" release is shown 
in Figure 34, with a diagram of the connections. The wind- 
ing of the magnet M^ carries the main current. When the 
current exceeds a certain amount (which can be regulated 
by a small nut) the armature below the magnet will 



MOTORS 



71 



be attracted, thus short circuiting the coil M and allowing 
the arm to fly back and shut off the current to the motor. This 
device cannot be considered to take the place of the regular 
cut-outs, as it is not operative during the starting of the motor. 
It can only operate after the arm A is held in position by the 
magnet M. 

Starting boxes are made in different designs to meet the re- 
quirements of the various classes of work on which they are 
used. Figure 35 shows a large automatic starting box where 
the resistance is cut out by the action of the solenoid S, which 




Figure 35 

draws up the movable arm. When solenoids are used for this 
purpose it is often advisable to arrange the connections so that 
when the movable arm has been raised to the highest and last 
point a resistance will be inserted in series with the solenoid 
to cut down the current and reduce the heating in the coil, 



72 



MODERN ELECTRICAL CONSTRUCTION. 



as less current is required to hold the arm in place than to 
move it over the contacts. Incandescent lamps are often used 
for this purpose and must be installed as in 4, Class A. 

A speed controller differs from a starting box mainly in 
the size of wire used as resistance. The resistance coils of a 




Fiffure 36 



Starting box are wound with comparatively small wire con- 
nected in circuit for a short time only, generally from ten to 
twenty seconds, while in a speed controller the wire must be of 
sufficient size to carry the current as long as the motor is run- 
ning. Another difference between the starting box and speed 
controller is the automatic coil, (Fig. 33) M, which in the 
speed controller is arranged to hold the arm A in any position 
in which it may be placed. This is accomplished in some types 
of speed controllers by a lever attached to an armature, which 



MOTORS 



73 



is attracted by the magnet M, the other end of the lever fitting 
into a series of indentations on lower part of movable arm. 

While the underwriter's rules do not require a speed con- 
troller to be automatic, still .it is good practice to make them 
so, as the same principles apply to the starting of a motor with 
a speed controller as with a starting box. 

Figure 36 shows a circuit breaker which is operative during 
the starting of the motor, and can be used to take the place of 
the switch required. 

As the arm of a starting box or speed controller is moved 
from one contact to another, more or less sparking results, 
and, as has already been stated, considerable heat is developed 
in the coils. A rheostat should never be located in a room 
where either inflammable gases or dust exist. If a starting box 
is to be located in a room where considerable dirt is apt to 
gather, or if the room is unusually damp, the starting box 
should be mounted in a dust-tight fire-proof box, which should 



~w~ 



lAA/V^ 



u\/\/\AI 



Figure 37 



be kept closed at all times, except when starting the motor. If 
the enclosing box is rather large, sufficient ventilation of the 
coils will be obtained while the motor is being started and the 
door open. A speed controller should never be mounted in an 
enclosure unless the same is arranged to give a thorough 
ventilation to the outside air, as heat is constantly being gen- 
erated in the coils of the rheostat, and this heat must be dis- 



74 MODERN ELECTRICAL CONSTRUCTION. 

sip'ated. A speed controller should never be located where dust 
or lint is apt to gather on it. If it is necessary to use one on 
a motor located in such a place, it should be mounted outside 
the room. 

In metal working establishments or in any place where there 
is a liability of the contacts on the switches or the starting 
boxes being short-circuited, they should be enclosed or suitably 
protected. 

e. Must not be run in series-multiple or multiple-series, 
except on constant-potential systems, and then only by special 
permission of the Inspection Department having jurisdiction. 

Figure 7)7 shows a series-multiple, and Figure 38 a multiple- 
series system of wiring. 

/. Must be covered with a waterproof cover when not in 



Figure 38 

use, and, if deemed necessary by the Inspection Department 
having jurisdiction, must be enclosed in an approved case. 

From the nature of the question the decision as to what is 
an approved case must be left to the Inspection Department 
having jurisdiction to determine in each instance. 

When it is necessary to locate a motor in the vicinity of 
combustibles or in wet or very dusty or dirty places, it is gen- 
erally advisable to surround it with a suitable enclosure. 

The sides of such enclosure should preferably be made 
largely of glass, so that the motor may be always plainly 
visible. This lessens the chance of its being neglected, and 
allows any derangement to be at once noticed. 

Under certain conditions it is found necessary to enclose 

motors in dust-tight enclosures. The practice of building a 

small box which fits entirely around the motor, enclosing the 



MOTORS 75 

pulley and provided with slots through which the belt passes, 
is very unsatisfactory. While this construction prevents con- 
siderable dust from settling on and around the motor, still a 
great deal will be carried in by the belt. If the box is so made 
that it fits tightly around the shaft between the pulley and the 
motor frame and is otherwise well constructed, most of the dust 
and dirt can be kept out. As the efficient working of the motor 
requires that it be kept as cool as possible, the box should 
afford sufficient ventilation. This may be obtained by making 
the box somewhat larger than the motor, thus allowing the heat 
to radiate from the sides, or the boxes should be ventilated to 
the outside air. 

A number of motors are so constructed that, by means of 
hand plates, they can be entirely enclosed. When they are so 
enclosed their efficiency and capacities are somewhat reduced, 
but cases are sometimes found where the conditions require 
motors of this kind to be used. 

In places where there is considerable dust flying about In 
the air, and w^here the dust Is not readily combustible, a fine 
gauze can be used to close the hand holes. This gauze will 
allow ventilation, but will prevent the dirt from gathering 
Inside the motor. The alternating induction motors, which are 
operated without brushes or collector rings, can be used in 
almost any location, as there Is no sparking. 

g. Must, when combined with ceiling fans, be hung from 
insulated hooks, or else there must be an insulator interposed 
between the motor and Its support. 

Ceiling fans are generally provided with an Insulating knob 
on which the fan hangs. If this Is not provided, a simple knob 
break can be used, or the fan can be suspended from a hook 
screwed into a hardwood block, provided the hook does not 
pass through the block into the plaster, the block being sep- 
arately supported from the ceiling. 

h. Must each be provided with a name-plate, giving the 



76 MODERN ELECTRICAL CONSTRUCTION. 

maker's name, the capacity in volts and amperes, and the nor- 
mal speed in revolutions per minute. 

9. Railway Power Plants. 

a. Each feed wire before it leaves the station must be 
equipped with an approved automatic circuit-breaker (see No. 
52) or other device, which will immediately cut off the current 
in case of an accidental ground. This device must be mounted 
on a fireproof base, and in full view and reach of the attendant. 

10. Storage or Primary Batteries. 

a. When current for light and power is taken from primary 
or secondary batteries, the same general regulations must be 
observed as apply to similar apparatus fed from dynamo gen- 
erators developing the same difference of potential. 

h. Storage battery rooms must be thoroughly ventilated. 

c. Special attention is directed to the rules for wiring in 
rooms where acid fumes exist (see No. 24, i to k). 

d. All secondary batteries must be mounted on non-absorp- 
tive, non-combustible insulators, such as glass or thoroughly 
vitrified and glazed porcelain. 

e. The use of any metal liable to corrosion must be avoided 
in cell connections of secondary batteries. 

Rubber-covered wire run on glass knobs should be used for 
wiring storage battery rooms. The knobs should be of such 
size as to keep the wire at least one inch from the surface wired 
over, and they should be separated 2^^ inches for voltage up 
to 300, and 4 inches for voltages over 300. Waterproof sockets 
hung from stranded rubber covered wire and properly sup- 
ported independently of the joints should be used; these lights 
to be controlled by a switch placed outside of battery room. 
All joints after being properly soldered and taped with both 
rubber and friction tape should be painted with some good 
insulating compound. This tends to keep all acid fumes away 
from the wire. 



TRANSFORMERS 77 

11. Transformers. 

(For construction rules, see No. 62.) 

(See also Nos. 13, 13 a, 36.) 

a. In central or sub-stations the transformers must be so 
placed that smoke from the burning out of the coils or the 
boiling over of the oil (where oil filled cases are used) could 
do no harm. 

If the insulation in a transformer breaks down, consider- 
ble heat is likely to be developed. This would cause a dense 
smoke, which might be mistp.ken for a fire and result in 
water being thrown into the building, and a heavy loss there- 
by entailed. Moreover, with oil cooled transformers, espe- 
cially if the cases are filled too full, the oil may become 
ignited and boil over, producing a very stubborn fire. 



J 



NOTICE— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CON- 
FLICTS WITH THESE RULES. 



Class B. 

OUTSIDE WORK. 

All Systems and Voltages. 



12. Wires. 



a. Service wires must have an approved rubber insulating 
covering (see No. 41). Line wires, other than services, must 
have an approved weatherproof or rubber insulating covering 
(see Nos. 41 and 44). All tie wires must have an insulation 
equal to that of the conductors they confine. 

In risks having- private generating- plants, the yard wires 
running from building to building- are not generally consid- 
ered as service wires, so that rubber insulation would not be 
required. 

By service wires are meant those wires which enter the 
building. It is customary to run the rubber-covered wire from 
the service switch and cutout inside of building through the 
outer walls, and to leave but a few feet of wire to which the 
line wires can later be spliced. This is illustrated in Figure 39, 
which shows how wires are run from pole to building. 

h. Must be so placed that moisture cannot form a cross 
connection between them, not less than a foot apart, and not 
in contact with any substance other than their insulating sup- 
ports. Wooden blocks to which insulators are attached must 
be covered over their entire surface with at least two coats of 
waterproof paint. 

c. Must be at least 7 feet above the highest point of flat 
roofs, and at least one foot above the ridge of pitched roofs 
over which they pass or to which they are attached. 

Roof structures are frequently found which are too low 
or much too lig-ht for the work, or which have been carelessly 



OUTSIDE WORK 



79 



put up. A structure which is to hold the wires a proper 
distance above the roof in all kinds of weather must not only 
be of sufficient height, but must be substantially constructed 
of strong- material 

It is well to avoid fastening wires perpendicular above one 
another, as in winter icicles may form which extend from the 
top to the lower wire, and the moisture on these will often 




Figure 39 

cause much trouble. The rule requires that wires be 7 feet 
above flat roofs, and roof structures must, therefore, be made 
high enough to allow for "sag." In moderately long runs 
2 or 3 feet will be sufficient. For long runs, see following table, 
taken from construction rules of Commonwealth Electric Com- 
pany of Chicago : 

The tension on wires should be such that the sag of a span 
of 125 feet will not exceed the amounts shown. 



20 30 



40 
10 



50 
10 



60 
12 



70 
12 



14 



90 
14 



Temperature, F. . . 10 
Sag, feet 6 

This table will also be useful to consult when running wires 
over housetops to which they are not attached, as it shows 
the variation in "sag" due to different temperatures. Wires 



MODERN ELECTRICAL CONSTRUCTION. 

should be so run that even at the highest temperature they will 
still clear the buildings. Allowance should also be made for 
the gradual elongation of the wire due to its own weight, giving 
way of supports or sleet that may at times weigh it down. 

d. Must be protected by dead insulated guard irons or 
wires from possibility of contact with other conducting wires 
or substances to which current may leak. Special precautions 
of this kind must be taken where sharp angles occur, or where 
any wires might possibly come in contact with electric light 
or power wires. 

Crosses, when unavoidable, should be made as nearly at 
right angles as possible. 

These guard wires are run parallel to and above the lower 
set of wires. Their object is to prevent the upper crossing 
wires, should they break, from coming in contact with the 
lower. A separate set of cross arms must be placed on the 
lower poles or above the lower wires to which the guard 
wires must be fastened. In Figure 40 1 and 2 show break in- 
sulators that may be used to electrically disconnect guard wires. 

e. Must be provided with petticoat insulators of glass or 
porcelain. Porcelain knobs or cleats and rubber hooks will 
not be approved. 

/. Must be so spliced or joined as to be both mechanically 
and electrically secure without sokier. The joints must then 
be soldered, to insure preservation, and covered with an 
insulation equal to that on the conductors. 

All joints must be soldered, even if made with some form 
of patent splicing device. This ruling applies to joints and 
splices in all classes of wiring covered by these rules. 

In Figure 40 single and double petticoat insulators are shown. 
It is very often convenient to fasten such insulators upside 
down or horizontally, but this should never be done, as they 
will then fill with water or dirt and their insulating qualities 
be destroyed. 

g. Must, where they enter buildings, have drip loops 
outside, and the holes through which the conductors pass must 



OUTSIDE WORK 



81 



be bushed with non-combustible, non-absorptive insuK ting 
tubes slanting upward toward the inside. 

h. Telegraph, telephone and similar wires must not be 
placed on -the same cross-arm with electric light or power 
wires, and when placed on the same pole with such wires 
the distance between the two inside pins of each cross-arm 
must not be less than 26 inches. 

i. The metallic sheaths to cables must be permanently 
and effectively connected to "earth." 

The telephone or telegraph wires are sometimes placed 
above the power wires, and it very often becomes necessary 






A 




o 



Figure 40 



for a lineman to pass through the lower wires to get at the 
upper. Great care is necessary to avoid coming in contact 
with high tension power wires while handling the telephone 
wires. 

Poles should not be set more than 125 feet apart; 100 or 
110 feet is good practice. For small wires poles with 6-inch 
tops are often used, but for heavier wires 7-inch tops are 
advisable. The tops of pole should be pointed, so as to 
shed water, and the whole pole be well painted. Steps should 
be placed so that the distance between any two steps on the 
same side is not over 36 inches ; these steps should all be the 
same distance apart, and should not extend nearer than 8 feet 
to the ground. All "gains" cut into poles should be painted 
before cross-arms are placed in them. Such places are more 



32 MODERN ELECTRICAL CONSTRUCTION. 

likely to hold moisture and rot than exposed parts. Wherever 
feed wires end or sharp angles occur, double cross-arms 
should be used, fastened on opposite sides of pole and bolted 
together. 

All bolts, lag screws, etc., should be galvanized. Poles 
should be set at least as far into the ground as shown in the 
following table : 



Length of pole. 


Depth in ground. 


35 feet 


5^ feet 


40 " 


6 


45 " 


6 


50 " 


6^ " 


55 " 


7 


60 " 


S 



The holes should be large enough to admit of thorough 
tamping on all sides of bottom of hole. If the tamping at 
bottom of hole is not well done, the pole will always be shaky, 
no matter how much tamping may be done at the top. If 
the ground is soft, the pole may be set in cement, or short 
pieces of planking fastened to it at right angles underground. 
At the end of line or where sharp bends occur, strong gal- 
vanized guy cables fastened to poles six or eight feet long, 
buried underground, should be used. 

Trolley Wires. 

y. Must not be smaller than No. B. & S. gage copper 
or No. 4 B. & S. gauge silicon bronze, and must readily stand 
the strain put upon them when in use. 

k. Must have a double insulation from the ground. In 
wooden pole construction the pole will be considered as one 
insulation. 

/. Must be capable of being disconnected at the power 
plant, or of being divided into sections, so that, in case of fire 
on the railway route, the current may be shut off from the 



OUTSIDE WORK 83 

particular section and not interfere with the work of the 
firemen. This rule also applies to feeders. 

m. Must be safely protected against accidental contact 
where crossed by other conductors. 

Guard wires should be insulated from the ground and 
should be electrically disconnected in sections of not more 
than 300 feet in length. 

Ground Return Wires. 

n. For the diminution of electrolytic corrosion of under- 
ground metal work, ground return wires must be so arranged 
that the difference of potential between the grounded dynamo 
terminal and any point on the return circuit will not exceed 
twenty-five volts. 

It is sug-g-ested that the positive pole of the dynamo be 
connected to the trolley line, and that whenever pipes or other 
underground metal work are found to be electrically positive 
to the rails or surrounding earth, that they be connected by 
conductors arranged so as. to prevent as far as possible cur- 
rent flow from the pipes into the ground. 

12 A. Constant-Potential Pole Lines, Over 5,000 Volts. 

(Overhead lines of this class unless properly arranged 
may increase the fire loss from the following causes : — 

Accidental crosses between such lines and low-potential 
lines may allow the high-voltage current to enter buildings 
over a large section of adjoining country. Moreover, such 
high voltage lines, if carried close to buildings, hamper the 
work of firemen in case of fire in the building. The object 
of these rules is so to direct this class of construction that 
no increase in fire hazard will result, while at the same time 
care has been taken to avoid restrictions which would un- 
reasonably impede progress in electrical development. 

It is fully understood that it is impossible to frame rules 
which will cover all conceivable cases that may arise in con- 
struction work of such an extended and varied nature, and it 
is advised that the Inspection Department having jurisdiction 
be freely consulted as to any modification of the rules in par- 
ticular cases.) 

a. Every reasonable precaution must be taken in ar- 



84 MODERN ELECTRICAL CONSTRUCTION. 

ranging routes so as to avoid exposure to contacts with other 
electric circuits. On existing lines, where there is a liability 
to contact, the route should be changed by mutual agreement 
between the parties in interest wherever possible. 

h. Such lines should not approach other pole lines nearer 
than a distance equal to the height of the taller pole line, 
and such lines should not be on the same poles with other 
wires, except that signalling wires used by the Company 
operating the high-pressure system, and which do not enter 
property other than that owned or occupied by such Com- 
pany, may be carried over the same poles. 

c. Where such lines must necessarily be carried nearer to 
other pole lines than is specified in Section b above, or where 
they must necessarily be carried on the same poles with 
other wires, extra precautions to reduce the liability of a 
breakdown to a minimum must be taken, such as the use of 
wires of ample mechanical strength, widely spaced cross-arms, 
short spans, double or extra heav}^ cross-arms, extra heavy 
pins, insulators, and poles thoroughly supported. If carried 
on the same poles with other wires, the high-pressure wires 
must be carried at least three feet above the other wires. 

d. Where such lines cross other lines, the poles of both 
lines must be of heavy and substantial construction. 

Whenever it is feasible, end-insulator guards should be 
placed on the cross-arms of the upper line. If the high- 
pressure wires cross below the other lines, the wires of the 
upper line should be dead-ended at each end of the span to 
double-grooved, or to standard transposition insulators, and 
the line completed by loops. 

One of the following forms of construction must then be 
adopted : 

1. The height and length of the cross-over span may 
be made such that the shortest distance between the 
lower cross-arms of the upper line and any wire 
of the lower line will be greater than the length 
of the cross-over span, so that a wire breaking 
near one of the upper pins would not be long 
enough to reach any wire of the lower line. The 
high-pressure wires should preferably be above the 
other wires. 



OUTSIDE WORK 85 

2. A joint pole may be erected at the crossing point, 

high-pressure wires being supported on this pole 
at least three feet above the other wires. Mechan- 
ical guards or supports must then be provided, so 
that in case of the breaking of any upper wire, it 
will be impossible for it to come into contact with 
any of the lower wires. 

Such liability of contact may be prevented by 
the use of suspension wires, similar to those em- 
ployed for suspending aerial telephone cables, 
which will prevent the high-pressure wires from 
falling in case they break. The suspension wires 
should be supported on high-potential insulators, 
should have ample mechanical strength, and should 
be carried over the high-pressure wires for one span 
on each side of the joint pole, or where suspension 
wires are not desired guard wires may be carried 
above and below the lower wires for one span on 
each side of the joint pole, and so spread that a 
falling high-pressure wire would be held out of 
contact with the lower wires 

Such guard wires should be supported on high- 
potential insulators or should be grounded. When 
grounded, they must be of such size, and so con- 
nected and earthed, that they can surely carry to 
ground any current which may be delivered by any 
of the high-pressure wires. Further, the construc- 
tion must be such that the guard wires will not 
be destroyed by any arcing at the point of contact 
likely to occur under the conditions existing. 

3. Whenever neither of the above methods is feasible, 

a screen of wires should be interposed between 
the lines at the cross-over. This screen should be 
supported on high tension insulators or grounded 
and should be of such construction and strength 
as to prevent the upper wires from coming into 
contact with the lower ones. 

If the screen is grounded each wire of the screen 
must be of such size and so connected and earthed 
that it can surely carry to ground any current 
which may be delivered by any of the high pressure 
wires. Further, the construction must be such that 
the wires of screen will not be destroyed by any 
arcing at the point of contact likely to occur under 
the conditions existing. 

e. When it is necessary to carry such lines near buildings, 
they must be at such height and distance from the building 
as not to interfere with firemen in event of fire; therefore, if 



86 MODERN ELZCTr.ICAL COXSTRUCTION. 

within 25 feet of a building, they n:i-st be carried at a height 
not less than that of the front cornice, and the height must be 
greater than that of the cornice, as the wires come nearer to 
the building, in accordance with the following table : — 

Distance of wire Elevation of wire 

from building. above cornice of building. 

Feet. Feet. 

25 

20 2 

15 4 

10 6 

5 8 

21/3 9 

It is evident that where the roof of the building continues 
nearly in line with the walls, as in Mansard roofs, the height 
and distance of the line must be reckoned from some part of 
the roof instead of from the cornice. 

13. Transformers. 

(For construction rules, sec No. 62.) 

(See also Nos. 11, 13 A and 36.) 

Where transformers are to be connected to high-voltage 
circuits, it is necessary in many cases, for best protection to 
life and property, that the secondary system be permanently 
grounded, and provision should be made for it when the trans- 
formers are built. 

a. Must not be placed inside of any building excepting 
central stations, unless by special permission of the Inspection 
Department having jurisdiction. 

An outside location is always preferable; first, because it 
keeps the high-voltage primary wires entirely out of the 
building, and second, for the reasons given in the note to 
No. 11 a. 

h. Must not be attached to the outside walls of buildings, 
unless separated therefrom by substantial supports. 

The alternating current transformer consists of an iron 
core upon which wires of two distinct electrical circuits are 
wound. One of these is known as the primary circuit, and in 
it the high pressure currents coming direct from the dynamo 
circulate. The other is known as the secondary circuit, and 
in it the low pressure currents used inside of buildings circu- 



GROUNDING 



87 



late. These two circuits are wound generally one over the 
other, and are very close together. The pressure used in the 
primary coil is from 1,000 to 5,000 volts, while in the secondary 
it is reduced usually to 110 or 220. 

It quite frequently happens that the insulation between the 
two windings breaks down and thus the high pressure is acci- 
dentally brought into buildings. Under such circumstances 
should any one touch any live part of the installation while 
touching also grounded parts of the building death would very 
likely result. Also, should there be a weak spot in the insula- 
tion, it is quite likely the high pressure would pierce it at that 
point with a possible result of a fire. Many deaths and fires 



' I IIS-230 ti 



E] 



y u|//^K 



@ 



n 230 \ 



E] 









11 11. 




JL JL 




M 1 


































































E 


3 


3 


f/ 


/ylSf 230 





=^ w 



m 



Figure 41 



have been caused in this way. If such lines are connected to 
ground the chances for harm are very much lessened, for the 
current will never take the path of high resistance 'through 
a man's body, while a direct path through a low resistance wire 
is open to it. 

It must not be supposed that "grounding" one side of an" 
electric light system is not often followed by serious conse- 



88 MODERN ELECTRICAL CONSTRUCTION. 

quences, for under such circumstances a ground coming on any 
other part of the system will cause a short circuit at once. 
The grounding in these cases is to be looked upon as the lesser 
of two evils rather than as an advantage. With alternating 
currents, the chances of possible damage from grounding 
are much less than with direct currents, because each trans- 
former with its small group of lamps is a system by itself and 
not affected by grounds on other transformers. Thus a 5,000 
light alternating current installation would consist of from 
25 to 50 separate systems, each independent of defects on the 
rest, while in a continuous current installation, a ground on the 
most remote branch circuit would in conjunction with a 
ground on the opposite pole of any other part of the system 
form a short circuit. 

Methods of grounding secondary wires of alternating cur- 
rent transformers are shown in Figure 41, taken from an 
instruction book issued by the Commonwealth Electric Com- 
pany of Chicago. 

In connection with 3-wire systems, grounding of the neutral 
wire can do little harm^ because ordinarily the neutral wire 
seldom carries much current, and that current is apt to vary 
in. direction so that the electrolytic effect will be on the whole 
quite negligible. 

There is, of course, the hazard brought about by the fact 
that a ground coming on one of the outside wires will imme- 
diately form a short-circuit in connection with the ground on 
the neutral. 

In connection with 3-wire systems, however, it is of the 
greatest importance (as more fully explained further on) that 
the neutral wire remain intact, and it being thoroughly 
grounded at all available outside places will help to keep it so. 

13 A. Grounding Low-Potential Circuits. 

The grounding of low-potential circuits under the follow- 



GROUNDING. 89 

ing regulations is only allowed when such circuits are so ar- 
ranged that under normal conditons of service there will be 
no passage of current over the ground wire. 

Direct-Current 3-Wire System. 

a. Neutral wire may be grounded, and when grounded 
the following rules must be complied with : — 

1. Must be grounded at the Central Station on a metal 

plate buried in coke beneath permanent moisture 
level, and also through all available underground 
water and gas-pipe systems. 

2. In underground systems the neutral wire must also be 

grounded at each distributing box through the box. 

3. In overhead systems the neutral wire must be 

grounded every 500 feet, as provided in Sections 
c, e, f and g. 

Inspection Department having jurisdiction may require 
grounding if thej'- deem it necessary. 

Two-wire direct-current systems having no accessible neu- 
tral point are not to be grounded. 

Alternating-Current Secondary Systems. 

. b. Transformer secondaries of distributing systems 
should preferably be grounded, and when grounded, the follow- 
ing rules must be complied with : — 

1. The grounding must be made at the neutral point or 

wire, whenever a neutral point or wire is accessible. 

2. When no neutral point or wire is accessible, one side 

of the secondary circuit may be grounded, pro- 
vided the maximum difference of potential between 
the grounded point and any other point in the circuit 
does not exceed 250 volts. 

3. The ground connection must be at the transformer 

as provided in sections d, e, f, g, and when trans- 
formers feed systems with a neutral wire, the neu- 
tral wire must also be grounded at least every 250 
feet for overhead systems, and every 500 feet for 
underground systems. 
Inspection Departments having jurisdiction may require 
grounding if they deem it necessary. 



90 MODERN ELECTRICAL CONSTRUCTION. 

Ground Connection. 

c. The ground wire in direct-current 3-wire systems must 
not at Central Stations be smaller than the neutral wire and 
not smaller than No. 6 B. & S. gage elsewhere. 

d. The ground wire in alternating-current systems must 
never be less than No. 6 B. & S. gage, and must always have 
equal carrying capacity to the secondary lead of the trans- 
former, or the combined leads where transformers are con- 
nected in parallel. 

On three phase sy.gtems, the ground wire must have a 
carrying capacity equal to that of any one of the three mains. 

c. The ground wire must be kept outside of buildings, but 
may be directly attached to the building or pole. The wire 
must be carried in as nearly a straight line as possible, and 
kinks, coils and sharp bends must be avoided. 

f. The ground connection for Central Stations, trans- 
former substations, and banks of transformers must be made 
through metal plates buried in coke below permanent mois- 
ture level, and connection should also be made to all available 
underground piping systems including the lead sheath of under- 
ground cables. 

g. For individual transformers and building services the 
ground connection may be made as in Section /, or may be 
made to water or other piping systems running into the build- 
ings. This connection may be made by carrying the ground 
wire into the cellar and connecting on the street side of meters, 
main cocks, etc., but connection must never be made to any 
lead pipes which form part of gas services. 

In connecting a ground wire to a piping system, the wire 
should, if possible, be soldered into a brass plug and the plug 
forcibly screwed into a pipe-fitting, or, where the pipes are 
cast iron, into a hole tapped into the pipe itself. For large 
stations, where connecting to underground pipes with bell 
and spigot joints, it is well to connect to several lengths, as 
the pipe joints may be of rather high resistance. Where plugs 
cannot be used, the surface of the pipe may be filed or scraped 
bright, tlie wire wound around it, and a strong clamp put 
over the wire and firmly bolted together. 

Where ground plates are used, a No. 16 Stubbs' gage 
copper plate, about three by six feet in size, with about two 
feet of crushed coke or charcoal, about pea size, both under 
and over it, would make a ground of sufficient capacity for a 



GROUND PLATES. 91 

moderate-sized station, and would probably answer for the 
ordinary substation or bank of transformers. For a large 
central station, a plate with considerably more area might 
be necessary, depending upon the other underground con- 
nections available. The ground wire should be riveted to 
the plate in a number of places, and soldered for its whole 
length. Perhaps even better than a copper plate is a cast- 
iron plate with projecting forks, the idea of the fork being 
to distribute the connection to the ground over a fairly broad 
area, and to give a large surface contact. The ground wire 
can probably best be connected to such a cast-iron plate by 
soldering it into brass plugs screwed into holes tapped in the 
plate. In all cases, the joint between the plate and the ground 
wire should be thoroughly protected against corrosion by 
painting it with waterproof paint or some equivalent. 



NOTE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class C. 

INSIDE WORK. 
All Systems and Voltages. 

GENERAL RULES. 

14. Wires. 

(For special rules, see Nos. i8, 24, 35, 38 and 39.) 

a. Must not be of smaller size than No. 14 B. & S. gage, 
except as allowed under Nos. 24 v and 45^. 

The exceptions being wires used inside of ^fixtures and 
flexible cord used to suspend individual electric lights. For 
general purposes a wire smaller than No. 14 is too easily 
broken, either through a sharp kink, or by drawing too tight 
with tie wires. To avoid trouble from kinks or sharp bends, 
wires smaller than 14 should preferably be stranded. 

h. Tie wires must have an insulation equal to that of the 
conductors they confine. 

This is considered necessary, because very often the tie 
wire cuts through the insulation of the wire it confines, and if 
the tie wire should come in contact with other than its insu- 
lating support, there would still be good insulation. In Figure 
42, (1) and (2) illustrate the method of tieing usually employed 
with small wires on insulators ; (4) shows a method employed 
with larger wires. This is also especially useful, because slack 
can be taken up if the tie wire is arranged to draw the main 
wire ^bout half way around the insulator; (6) shows a knot 
tied into the wire, as is usual where the end of the wire 



INSIDE WORK. 



93 



connects into cut-outs or switches. At (5) insulators are 
arranged to hold large wires. It is not advisable to tie large 
wires to insulators, as the weight of the wire will soon cause 




Figure 42 

it to cut through the insulation. Cleats, such as shown at (8) 
and (9), are preferable. 

c. Must be so spliced or joined as to be both mechanically 
and electrically secure without solder. The joints must then 



94 



MODERN ELECTRICAL CONSTRUCTION. 




Figure 43 



INSIDE WORK. 95 

be soldered to insure preservation, and covered with an insu- 
lation equal to that on the conductors. 

Stranded wires must be soldered before being fastened 
under clamps or binding screws, and whether stranded or 
solid, when they have a conductivity greater than that of No. 
8 B. & S. gage they must be soldered into lugs for all terminal 
connections. 

All joints must be soldered, even if made with some form 
of patent splicing device. This ruling- applies to joints and 
splices in all classes of wiring covered by these rules. 

At the left on top of Fig. 43 is shown the well-known 
Western Union joint. Before joining wires they should be 
thoroughly cleaned by scraping with the back of a knife or 
sand or emery paper. The insulation should be removed, as 
indicated at Z?; if it is cut into as at a, it is very likely that 
the wire will be "nicked" and will be likely to break at that 
point. It is also more difficult to tape a joint properly if the 
rubber has been cut in this way than it is with the rubber cut 
as at b. After the joint has been made it is covered with 
soldering fluid, a formula for which is given below. In lieu 
of this there are soldering sticks and salts, already prepared, 
on the market. 

The following formula for soldering fluid is sug- 
gested : — ■ 

Saturated solution of zinc chloride 5 parts 

Alcohol 4 parts 

Glycerine 1 part 

The joint having been thoroughly covered with one of 
these preparations is next heated with a gasoline or alcohol 
torch and a small piece of solder allowed to melt on it near 
the center. It is well to avoid heating too much at the ends 
of the joint, as it weakens the wire. After the joint is cool, 
wipe off all moisture and cover with layers of rubber tape, 
enough, at least, so that it is equal in thickness to the rubber 
insulation on the wire used, as shown at a and b. This rubber 



96 MODERN ELECTRICAL CONSTRUCTION. 

tape is then covered with friction tape to keep it in place. 
Before taping joints the outer braid of the wire should be 
carefully skinned back. If any of the cotton threads of which 
it consists were to be left in contact with the bare wire, they 
would, when moist, form a leak, which might prove trouble- 
some. If joints are exposed to the weather it will be well to 
paint them over with some insulating paint to keep the friction 
tape in place, as it will otherwise soon work loose when it 
becomes dry. 

At c and d "tap" joints are shown. The method shown 
at d is preferable, because the wire cannot easily work loose. 
The method of joining shown at e is useful when, for instance, 
two wires, each of which is fastened to an insulator, are to be 
joined. The wires c?n be drawn very tight in this way. 
This sort of joint is very common in fixture work, and should 
be finished off as at /. 

Twin wires other than flexible cord are allowed only in 
metal conduits, and joints in them, should be made only within 
the junction boxes. When joints in conduit are unavoidable, 
twin wires should be joined as at g, so that the joints are not 
opposite each other. Joints in flexible cord should be avoided 
as much as possible. 

In splicing stranded wires it is customary to remove some 
of the center strands to avoid making a very bulky splice. All 
stranded wires must be soldered where fastened under binding 
screws; this refers also to flexible cord used in sockets. The 
best way to solder the ends of cords is to dip them in melted 
solder; a blow torch will easily overheat small wires and 
leave them brittle. 

Figure 44 shows lead covered wire spliced and taped. In 
handling lead covered wire great care must be exercised 
(especially with paper insulated) that it be not bruised and the 
lead not punctured. The lead covering is of use only as a 
protection against water; if it admits the least bit of moisture 



INSIDE WORK. 97 

it is worse than useless. The ends of lead covered wires 
should always be kept sealed until ready for use ; in damp 
places the paper insulation may absorb moisture, which will 
ground the wire on the lead. When installed the ends should 
always be sealed against moisture. Lead covered v/ires 
should never be used where there is a liability of nails being 
driven into them. 

Joints in lead covered wires are made just as in ordinary 
wires. Extreme care is necessary that no moisture be left on 




Figure 44 

the wire when it is taped or covered up. Before the wire is 
joined a sleeve (Figure 44) is slipped over one of the wires. 
After the joint has been made and taped, this sleeve is placed 
so as to cover it, and the ends split and arranged to fit close 
against the lead on the wires. That part of the lead which 
must be soldered to make the joint watertight is scraped until 
it is perfectly bright and then coated with tallow candle grease. 
It can then be soldered with an iron, or melted solder can be 
poured on it and wiped around it, as plumbers do. If a 
soldering iron is used it must not be too hot, and not allowed 
to remain in one place too long, as the lead itself melts at 
nearly the same temperature as the solder. An inexperienced 
workman may burn more holes into the lead than he closes. 
If a neat job is desired, that part of the lead which is to be kept 
free of solder is covered with lampblack and glue, or ordinary 
paper hanger's paste, or a mixture of flour and water boiled, 
so as to prevent the solder from taking on it. 

d. Must be separated from contact with walls, floors, 
timbers or partitions through which they may pass by non- 



98 



MODERN ELECTRICAL CONSTRUCTION. 



combustible, non-absorptive insulating tubes, such as glass or 
porcelain, except as provided in No. 24 u. 

Bushing-s must be long- enoug-h to bush the entire length 
of the hole in one continuous piece or else the hole must 
first be bushed by a continuous waterproof tube. This tube 
may be a conductor, such as iron pipe, but in that case an 
insulating- bushing must be pushed into each end of it, ex- 
tending far enough to keep the wire absolutely out of contact 
with the pipe. 

The exception mentioned is in regard to wires at outlets 
where they are required to be in approved flexible tubing from 
the last insulator to at least one inch beyond plaster, or end 
of the cap on gas piping. This is shown in Figure 45. The 
reason for the separation of wires from everything but their 
insulating supports are many. Should a bare live wire come 
in contact with damp woodwork or masonry, there would 




loom 




0= 



Figure 45 

very likely be some flow of current to ground and through the 
ground to the other pole of the dynamo or other wire. This 
flow of current may gradually char the woodwork, and in 
time start a fire ; or it may gradually eat away the wire, finally 
causing it to break. When a wire is eaten away, as shown 



INSIDE WORK. 



99 



at c and e, Figure 46, if it is carrying much current, the thin 
part will become very hot and will set fire to whatever inflam- 
mable material may be near it. If the current flow to the 
ground continues, the positive wire will finally be entirely 
severed, and an arc, similar to that noticed in an ordinary arc 
lamp, will be established, and will continue until the wire has 




Figure 46 

been burned away and the space between the two ends becomes 
too great for the arc to maintain itself. The negative wire, 
to which the current flows, is not eaten away in this manner, 
and such current flow is only possible when two wires of a 
system are in electrical connection with the ground. This 
action may, however, occur, even if the two grounded wires 
are miles apart. Wires and gas pipes are often destroyed 
through intermittent contact; for instance, if a wire makes a 
good contact to a gas pipe and there is a small leak to the pipe 
no particular harm will be done as long as the contact remains 
good. Should, however, the contact be intermittent, there will 
be a small arc at each break, and this will, little by little, burn 
holes into the gas pipe and into the wire. This action will 
take place on either a positive or negative wire. Non-com- 



\..<^\t:^. 



100 MODERN ELECTRICAL CONSTRUCTION. 

biistible supports for wires are farther useful in that they 
tend to prevent flames from the rubber insulation (which is 
very easily ignited from any of the above causes) from spread- 
ing to surrounding material. 

Figure 46 consists of copies of specimens showing effects 
of electrolysis, short circuits, and heating of lamp. These 
illustrations are copied from fire reports of the National Board 
of Underwriters. 

At a is shown a piece of gas pipe, which had been subject 
to electrolytic action until finally a hole had been eaten 
through the metal ; & is a socket which had been short cir- 
cuited, and the excessive damage was due to overfusing ot 
circuit. 

At c and e, the effects of electrolysis on wire are shown; 
r is a piece of underwriter's wire (not approved in moulding), 
which had been used in damp moulding, the leak to ground 
through the dampness causing the gradual eating away of the 
wire ; c shows a breakdown in the insulation and subsequent 
electrolytic action on the wire, causing it finally to break. 
This wire had been used in a round-house, where the sulphur 
fumes and the condensation of escaping steam on insulators 
had formed a path to ground. At d is an incandescent lamp 
which had been covered with a towel, the confined heat soft- 
ening the glass and setting fire to the towel. The danger of 
fire from overheated lamps is much greater than is generally 
supposed. Small lamps and lamps subject to a little excess 
of voltage are especially dangerous, and many instances are 
on record where they have charred woodwork and set fire 
to cloth or paper shades. 

. It may in many cases seem unnecessary to have bushings 
in one piece long enough to pass through a floor, or wide 
wall; but especially in passing through floors, it is very easily 
possible for wires to become crossed between the joists; that 
is, the wire entering at the right above the floor may be 



INSIDE WORK. 



101 



brought out at the left below the floor and the other wire 
through the opposite holes. In such a case the two wires of 
opposite polarity will be in contact, and should the insulation 
give out from any cause whatever, such as abrasion, or the 
gnawing of rats and mice, there would be nothing to prevent 
a short circuit and consequent fire. In passing through floors 
or walls the wires often come in contact with concealed pipes 
or other grounded material, so that only by making the bush- 
ings continuous can the wires be properly protected. 

Figure 48 shows short bushings arranged in iron pipe. 
Figure 49 shows a case where there is an offset in the wall. 
Cases of this kind very often occur. Sometimes the floor can 
be taken up and an iron conduit, properly bent, put in place ; or 
the wires placed on insulators. In this latter case the floor 
must not be put down until the inspector has examined the 
wires. The wires may be run on top of the floor to such a 
place where a continuous bushing may be dropped through 




Figure 47 Figure 48 Figure 49 

the floor. The wires on top of the floor must be then pro- 
tected by a suitable boxing or at least the same dimensions as 
given for boxing on side walls. 

e. Must be kept free from contact with gas, water or other 
metallic piping, or any other conductors or conducting ma- 



102 



MODERN ELECTRICAL CONSTRUCTION. 



terial which they may cross, by some continuous and firmly 
fixed non-conductor, creating a separation of at least one inch. 
Deviations from this rule may sometimes be allowed by spe- 
cial permission. 

When one wire crosses another wire the best and usual 
means of separating- them is by means of a porcelain tube on 
one of them. The tube should be prevented from moving out 
of place, either by a cleat at each end, or by taping it securely 
to the wire. 

The same method may be adopted where wires pass close 
to iron pipes, beams, etc., or, where the wires are above the 
pipes, as is generally the case, ample protection can frequently 
be secured by supporting the wires well with a porcelain cleat 
placed as nearly above the pipe as possible. 

Figure 50 is a sectional view of the manner in which wires 
are usually run through joists in bushings. For small wires 
bushings should preferably be installed as shown at top ; never 
as shown in the middle row. For larger wires the holes must 




Figure 50 

be bored as straight as possible; otherwise it will be difficult 
to pull wires through. The quantity of wire needed is also 
somewhat increased by slanting the holes. In open places 
wires are generally installed on insulators as shown in Fig- 
ure 51. 

Figure 51 shows different methods employed where one 
wire crosses another. The method at the left, which is more 
suited to large stiff wires, does not quite comply with the rule, 
but is very often used. The other two methods are preferable. 
Insulating supports should always be provided at the place 
of crossing to prevent the upper wires from sagging and 
resting on the lower; also to prevent any strain from coming 
on tap joints. Approved flexible tubing such as circular loom 



INSIDE WORK. 



103 



is also often used in crossing wires and pipes. In dry loca- 
tions it is quite safe and does not break as easily as tubes, 
but should never be used where there is any likelihood of 
dampness. 

f. Must be so placed in wet places that an air space will 
be left between conductors and pipes in crossing, and the 




Figure 51 



former must be run in such a way that they cannot come in 
contact with the pipe accidentally. Wires should be run over 
rather than under pipes upon which moisture is likely to 
gather or which, by leaking, might cause trouble on a circuit. 

This is a rule that is very often violated, as much work is 
done using loom, as shown at the left of Figure 52, and is 
quite safe with gas pipes. With cold water pipes, which are 



^^^^r^^^^^^u^ 



Figure 52 



likely to sweat, or with steam pipes, it is very bad practice. 
Where pipes are close against a ceiling it is better either to 
fish over them or drop wires some distance below them as 



104 MODERN ELECTRICAL CONSTRUCTION. 

illustrated at the right of the figure. No part of the wiring 
should be in contact with pipes. On side walls where ver- 
tical wires run across horizontal pipes the only safeguard 
would be to box the pipes and run the moisture to one side. 
The most harm is done by water on the insulators. If these 
can be kept dry it does not matter much about wires which 
hang free in the air. Whatever form of insulation is used 
in crossing pipes, it must be continuous. Short bushings 
strung on the wire, where a large pipe or number of pipes 
are being crossed, is not satisfactory, as the bushings are 
apt to separate or moisture gather in the space between them. 
The insulation must also be firmly attached to the wires. If 
knobs are not used as shown in Figure 51 to keep the bush- 
ings in place, they must be taped to the wire. 

g. The installation of electrical conductors in wooden 
moulding or where supported on insulators in elevator shafts 
will not be approved, but conductors may be installed in such 
shafts if encased in approved metal conduits. 

Wires supported on insulators in such places are very likely 
to be disturbed, especially in freight elevators. . Moulding is 
often so impregnated with oil, and the draft in an elevator 
shaft is usually so strong that a blaze once started would 
quickly run to the top. 

15. Underground Conductors. 

a. Must be protected against moisture and mechanical 
injury where brought into a building, and all combustible 
material must be kept from the immediate vicinity. 

b. Must not be so arranged as to shunt the current 
through a building around any catch-box. 

By reference to Figure 53 the meaning of this rule will 
be made clear. With wires run as shown it would be easy 
for any one having disconnected one service switch to believe 
all wires in the building dead, while they were in reality, still 
being kept alive by the other switch. 



INSIDE WORK. 



105 



c. Where underground service enters building through 
tubes, the tubes shall be tightly closed at outlets with asphalt- 
um or other non-conductor, to prevent gases from entering 
the building through such channels. 

d. No underground service from a subway to a building 
shall supply more than one building except by written permis- 
sion from the Inspection Department having jurisdiction. 



17. Switches, Cut-Outs, Circuit-Breakers, Etc. 

{For construction rules sec Nos. 51, ^2 and 53.) 

a. Must, unless otherwise provided (for exceptions, see 
No. 8 c and No. 22 c), be so arranged that the cut-outs will 
protect, and the opening of a switch or circuit-breaker will 



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disconnect, all of the wires ; that is, in a two-wire system the 
two wires, and in a three-wire system the three wires, must be 
protected by the cut-out and disconnected by the operation of 
the switch or circuit breaker. 

The exceptions are in regard to motors of 54 K- ?• or 
less on circuits of not over 300 volts and incandescent cir- 
cuits of not over 660 watts where single pole sv/itches are 
allowed. This rule forbids the practice, as sometimes em- 



106 



MODERN ELECTRICAL CONSTRUCTION. 



ployed on switchboards, of breaking the two outside wires of 
a 3-wire system and leaving the neutral, which is not carried 
through the switch, always connected. 

In connecting double-pole snap switches the wireman 
should be very careful. Most of these switches cross polari- 
ties as shown in Figure 54, and if connected wrong will form 
short circuits. Many of them have been connected that way, 
even by wiremen of some experience. 

h. Must not be placed in the immediate vicinity of easily 
ignitable stufif or where exposed to inflammable gases or dust 
or to flyings of combustible material. 

In starch and candy factories, grain elevators, flouring 
mills, and buildings used for woodworking or other purposes 
which would cause the fittings to be exposed to dust and flyings 
of inflammable material, the cut-outs and switches should be 
placed in approved cabinets outside of the dust-rooms. If, 
however, it is necessary to locate them in the dust-rooms, the 
cabinets must be dust-proof and must be provided with self- 
closing doors. 

Whenever an electric current is broken, whether by fuse 
or switch, an arc varying with the current strength, is 





Figure 54 



Figure 55 



Figure 56 



formed. Should a switch be only partly opened, this arc 
will continue and consume the metal of the switch until the 
gap in which it burns becomes too long, when the current 
will be broken. Meanwhile there is much heat generated 



INSIDE WORK. 107 

which may readily communicate to inflammable material 
nearby. 

There seems to be no reason except economy of wire why 
cut-outs should ever be placed inside of dust rooms. Switches 
of course must often be placed in such rooms as in many 
cases the entire building outside of the engine room is dusty. 
In such cases the switches as well as the cutouts may, how- 
ever, be often placed on the outside walls convenient to some 
window. 

An approved cabinet is shown in Figure 55. If used in 
connection with knife switches it should be large enough to 
admit being closed when the switch is open. In cases where 
cut-outs and switches must be located in dusty rooms, it 
would be well to construct double cabinets, one part for the 
cut-outs and another for the switches. The fuses, which are 
the most dangerous can then be tightly enclosed, as it will 
seldom be necessary to get at them. In practice it has been 
found almost impossible to keep the doors of cabinets which 
are much used closed. It seems next to impossible to con- 
struct a cabinet which is dust proof, with a door that can be 
readily opened, and a self-closing door can hardly be made 
to remain dustproof. Doors are made self-closing either 
through gravity or by suitable springs.. 

As switch and cut-out boxes are very likely to be used for 
the storage of cotton waste, paper, etc., which would readily 
ignite from a melted fuse, it would be well to construct them 
with a slanting bottom as indicated by the dotted line in Fig- 
ure 56, so that nothing will lie in them. 

c. Must, when exposed to dampness, either be enclosed 
in a waterproof box or mounted on porcelain knobs. 

Figure 56 is a sectional side view of a cut-out box for use 
out of doors. In it the switch is mounted on porcelain knobs. 
In all damp places much trouble is experienced from leakage 
through the moisture on the surface of the slate or marble 



108 



MODERN ELECTRICAL CONSTRUCTION. 



and through the wax used to cover the bare parts on back of 
switch. 

d. Time switches must be enclosed in an iron box or 
cabinet lined with fire resisting material. 

If an iron box is used, the minimum thickness of the iron 
must be 0.128 of an inch (No. 8 B. & S. Gauge). 

If the cabinet is used, it must be lined with marble or 
slate at least % of an inch thick, or with iron not less than 
0.128 of an inch thick. Box or cabinet must be so constructed 
that when switch operates blade shall clear the door by at 
least one inch. 



CONSTANT-CURRENT SYSTEMS. 



18. Wires. 



PRINCIPALLY SERIES ARC LIGHTING. 



(See also Nos. 14, 15 and 16.) 



a. Must have an approved rubber insulating covering (see 
No. 41). 

h. Must be arranged to enter and leave the building 
through an approved double-contact service switch (see No. 
51 &), mounted in a non-combustible case, kept free from mois- 
ture, and easy of access to police or firemen. 

In order that all of the wiring in the building may be 
entirely disconnected a switch, the principle of which is ilius- 




Figure 57 
trated at d, Figure 57, is provided where wires enter and 
leave the building. A modern commercial form of this switch 
is shown in Figure 58. This switch never breaks the circuit. 
As shown in Figure 57, the current passes from the positive 
pole, through the upper blade of the switch to h and thence 



CONSTANT CURRENT SYSTEMS. 



109 



through the arc lamps back to c and to the negative pole. 
When it is desired to extinguish the lamps the two blades of 
the switch are moved downward, as indicated by the dotted 
lines. The contacts d are arrans^ed so that both switch blades 
connect with them before disconnecting entirely from the 
points b and c. As soon as both blades are in contact with d 
all current flows through it because the resistance of it is 
so very much less than that of the lamps. With the switch in 
the position indicated by dotted lines, the current still flows 
in the outside wires, but all wires within the building are 
"dead." At c, Figure 57, is shown a single-pole switch which 
operates on the same principle as the other. If this switch is 
closed all current will pass through it ; if open the current will 
pass through the last 
lamp. A switch of this 
kind is always arranged 
within the lamp •itself. 
This latter way of 
switching lamps should 
never be used, as a lamp 
switched in this way is 
never safe to handle. 
There is just as much 
danger from shocks 
when the lamp is 
switched off as when on. 
With switches as de- 
scribed above there is no 

spark whatever when lamps are switched ofif, but there is usu- 
ally quite a spark when the lamps are switched in. Should there 
be a broken wire or a lamp out of order in the circuit to be 
switched in, there will be quite an arc maintained for some 
time. In such a case the switch should be quickly closed and 
the trouble located. 




Fig. 58. 



110 MODERN ELECTRICAL CONSTRUCTION. 

In handling live wires of this system great care is neces- 
sary. The wireman should insulate himself from the ground 
by a dry board, or, if all about him is damp, by a board resting 
on insulators. Rubber gloves and rubber boots, if kept dry, 
are useful. 

Death or bad burns may result if the wireman, standing on 
wet ground or any conductor in connection with it, touches 
part of a circuit which is also partly in connection with the 
ground. If, in Figure 57, the wire at / is grounded, a man in 
connection with the ground and touching a bare wire at h will 
receive a shock due to about 50 volts, but if he touches the 
wire at g, he will receive a shock of about 150 volts. The 
shock received from a line containing 100 lamps may be any- 
thing from 50 to 5,000 volts, and may result in only a slight 
burn or in instant death. 

Another danger in connection with live circuits is the lia- 
bility of cutting oneself into circuit. If one is perfectly 
insulated from the ground there is no harm whatever in touch- 
ing one live wire (with very high voltages such insulation is, 
however, hard to obtain) with either one or both hands while 
the wires are in order. Should, however, the wire between 
the two hands break, the current would immediately pass 
through the body, very likely causing instant death. Even if 
the circuit is not entirely broken, if only a resistance is cut in, 
the shock will be very severe. As, for instance, if one should 
touch the terminal of an arc lamp, not burning, with each hand 
nothing whatever would be felt, but, if the lamp were now 
suddenly switched on, there would be a very severe shock at 
first, which would become less so when the lamps were fairly 
started. To avoid the possibility of such occurrences when 
working on live lamps or circuits a short wire known as a 
"jumper" is often connected, as at k, Figure 57. This will 
carry all current, and there is now no danger except from a 
connection to ground. 



CONSTANT CURRENT SYSTEMS. Ill 

c. Must always be in plain sight, and never encased, except 
when required by the Inspection Department having juris- 
diction. 

What is known as concealed knob and tube work is not 
allowed in wiring for H. T. arcs ; neither can the wires be 
run in moulding or conduit. 

It has been customary to use no smaller than No. 6 wire 
for these high tension series circuits. The current required 
is seldom more than 10 amperes, and No. 14 wire has sufficient 
carrying capacity, but its mechanical strength is not very 
great. The danger from a broken wire in high tension sys- 
tems is much greater than in low tension systems, because of 
the long arc which occurs at the break. The loss in volts per 
100 feet with No. 6 will be about A, while with No. 14 it will 
be 2.6. This, however, will not affect the lights, because the 
pressure at the machine must be correspondingly increased. 

d. Must be supported on glass or porcelain insulators, 
which separate the wire at least one inch from the surface 
wired over, and must be kept rigidly at least eight inches from 
each other, except within the structure of lamps, on hanger- 
boards or in cut-out boxes, or like places, where a less distance 
is necessary. 

An extra precaution often taken in this kind of work on 
plastered walls is to place a wooden block or rosette about three 
inches in diameter and one-half inch thick under each insu- 
lator; this secures greater separation from ceilings and side 
walls and adds greatly to the stability of the insulators. On 
plastered walls a small insulator, if subjected to side strain, 
will cut into the plaster on one side and allow the wires to sag, 
the wooden block will prevent this. 

e. Must, on side wall, be protected from mechcnical injury 
by a substantial boxing, retaining an air space of one inch 
around the conductors, closed at the top (the wires passing 
through bushed holes), and extending not less than seven 
feet from the floor. When crossing floor timbers in cellars, 
or in rooms where they might be exposed to injury, wires 



112 



MODERN ELECTRICAL CONSTRUCTION. 



must be attached by their insulating supports to the under 
side of a wooden strip not less than one-half an inch in thick- 
ness. Instead of the running-boards, guard strips on each 
side of and close to the v/ires will be accepted. These strips 
to be not less than seven-eighths of an inch in thickness and 
at least as high as the insulators. 

Except on joisted ceilings, a strip one-half of an inch 
thick is not considered sufficently stiff and strong-. For spans 
of say eight or ten feet, where there is but little vibration, 
one-inch stock is generally sufficiently stiff; but where the 
span is longer than this or there is considerable vibration, 
still heavier stock should be used. 

For general suggestions as to protecting wires on side 
walls, see notes under No. 24 e. 

Figure 59 is an illustration of protection on side walls, 

giving the dimensions required. The wooden block shown, 

which raises bushings above floor, is an extra protection to 

1 



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ii • 4 




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Ml 


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Figure 59 
prevent water from running into them. The iron pipe is 
shown extending in one piece clear through the floor. With 
voltages used in this system a separate pipe should be pro- 
viucd for each wire, unless alternating currents are used. 



CONSTANT CURRENT SYSTEMS. 113 

19. Series Arc Lamps. 

(For construction rules, sec No. 57.) 
a. Must be carefully isolated from inflammable material. 

h. Must be provided at all times with a glass globe sur- 
rounding the arc, and securely fastened upon a closed base. 
Broken or cracked globes must not be used. 

c. Must be provided with a wire netting (having a mesh 
not exceeding one and one-fourth inches) around the globe, 
and an approved spark arrester (see No. 58), when readily 
inflammable material is in the vicinity of the lamps, to prevent 
escape of sparks of carbon or melted copper. It is recom- 
mended that plain carbons, not copper-plated, be used for 
lamps in such places. 

Outside arc lamps must be suspended at least eight feet 
above sidewalks. Inside arc lamps must be placed out of 
reach or suitably protected. 

Arc lamps, when used in places where they are exposed to 
flying-s of easily inflammable material, should have the car- 
bons enclosed completely in a tight globe in such manner as 
to avoid the necessity for spark arresters. 

"Enclosed arc" lamps, having tight inner globes, may be 
used, and the requirements of Sections b and c above would 
of course, not apply to them, except that a wire netting 
around the inner globe may in some cases be required if the 
outer globe is omitted. 

d. Where hanger-boards (see No. 56) are not used, lamps 
must be hung from insulating supports other than their con- 
ductors. 

At the left, Figure 60 is shown, the usual method of sus- 
pending outdoor arc lamps on buildings. The supporJ:ing wire 
may be fastened to brick or stone walls by drilling a hole about 
four inches deep and plugging this securely with wood, when 
an eye or lag bolt or large spike may be driven or screwed into 
it. Expansion bolts, of which there are many kinds to be had, 
may also be used. It is best to arrange the supporting wires 
at quite a high angle, otherwise the direct outward pull may 
be too great. Some of the older arc lamps are not provided 
with insulators, and may be suspended, as shown in the center 
of the figure. On very low ceilings, lamps are often arranged 



114 



MODERN ELECTRICAL CONSTRUCTION. 



as shown at the right, the plastering being cut away and lamp 
suspended from floor above joists. The space above plaster 




Figure 60 
must be enclosed on all sides and all v/oodwork protected 
with asbestos board at least one-eighth inch thick. 

If this method is used with constant potential arc lamps 
carrying resistance in the hood, it would be well to remove 
or short-circuit this resistance and locate another in a more 
suitable place. 

20. Incandescent Lamps in Series Circuits. 

a. Must have the conductors installed as required in No. 
18, and each lamp must be provided with an automatic cut-out. 

h. Must have each lamp suspended from a hanger-board 
by means of rigid tube. 

c. No electro-magnetic device for switches and no mul- 
tiple-series or series-multiple system of lighting will be 
approved. 

d. Must not under any circumstances be attached to gas 
fixtures. 

CONSTANT-POTENTIAL SYSTEMS. 

GENERAL RULES — ALL VOLTAGES. 

21. Automatic Cut-Outs (Fuses and Circuit-Breakers). 

(See No. 17, and for construction, Nos. 52 and S3-) 
Excepting on main switchboards, or where otherwise sub- 



CONSTANT POTENTIAL SYSTEMS. 115 

ject to expert supervision, circuit-breakers will not be ac- 
cepted unless fuses are also provided. 

The cut-out is the principal protective device used in elec- 
tric light and power work. In its simplest form it consists of 
a piece of wire made of a certain alloy designed to melt at 
a comparatively low temperature and so connected that all 
current used in a certain circuit must pass through it. We 
have already seen that currents of electricity generate heat in 
the conductors through which they pass, and that this heat 
is proportional to the square of the current flowing; that is, 
if we double the current we shall increase the production of 
heat fourfold. A dangerous rise in current strength may 
be due to a "short circuit' or to an overload, too many lamps 
or motors being connected to a circuit. To prevent damage 
to wires and other apparatus from excessive currents, fuses 
or cut-outs must be installed. When the current rises above 
its allowed strength the fuse melts and opens the circuit; 
that is, stops all current flow. This melting of the fuse is 
always accompanied by a flash of fire, called an arc, and 
may easily set fire to inflammable material located near the 
fuses. In the case of large fuses pieces of molten lead are 
often spattered about. 

Another device used for the same purpose as the fuse 
or cut-out is known as the circuit-breaker. A circuit-breaker 
in its simplest form comprises a knife switch which when 
closed is forced in against a spring and held in place by 
means of a small catch. A solenoid, inside of which is placed 
a moveable iron core, is connected in series with one side of 
the switch. When the current passing through this solenoid 
exceeds a certain amount, the iron core is drawn up into it, 
and, striking against the catch, releases the switch which will 
then fly open, thus cutting off the current. The core of this 
solenoid is so designed that when it starts to move its speed 
is greatly accelerated so that it strikes the catch a sharp 



116 



MODERN ELECTRICAL CONSTRUCTION. 



blow. By means of a small adjusting screw the circuit break- 
er can be set to operate at various current strengths within 
its limits. For this reason and for the further reason that 
it is so easily made inoperative by tying or blocking its sol- 
enoid it is not approved for general use unless fuses are also 
installed. It may be used under the care of a competent elec- 
trician who understands the dangers of its abuse. 

a. Must be placed on all service wires, either overhead 
or underground, as near as possible to the point where they 
enter the building and inside the walls, and arranged to cut 
off the entire current from the building. 

Where the switch required by No. 22 is inside the build- 
ing, the cut-out required by this section must be placed so 
as to protect it. 

In risks having private plants, the yard wires running 
from building to building are not generally considered as ser- 
vice wires, so that cut-outs would not be required where the 
wires enter buildings, provided that the next fuse back is 
small enough to properly protect the wires inside the building 
in question. 

The fuse block here required serves a double purpose ; it 
affords protection to the whole installation while in use, and 
is an effective means of disconnecting a building when cur- 
rent is no longer used. This can also be accomplished by 
means of the service switch, but a switch 
is so easily closed by anyone that it must 
never be relied upon entirely for this 
purpose. 

Figure 61 shows arrangement of fuses 
and switch as commonly installed where 
wires enter buildings. The wires enter at 
the top, connect to the fuse terminals, cur- 
rent passing through the fuses to the 
switch. 

h. Must be placed at every point Fig. 61. 




CONSTANT POTENTIAL SYSTEMS. 117 

where a change is made in the size of wire [unless the cut- 
out in the larger wire will protect the smaller (see No. 61)]. 

Figure 62, A to D, shows systems of distribution and ar- 
rangement of mains in general use. Figure A shows the 
simplest and cheapest method of running mains, and is 
known as the "tree system." Beginning at the service the 
wires must be large enough to carry the whole current to the 
first floor or wherever the first cut-out center is located. 
At this point the size of wire may be reduced because it will 
be required to carry only the current used further on. Main 
cut-outs should be arranged as shown in the figure at 1 
and 2. That is, the cut-outs protecting the mains must be in- 
stalled in the mains at each floor after the current for that 
floor has been taken off. Cases are often found where the 
cut-out is placed in the main line ahead of the branch blocks. 
This is obviously wrong, as the fuse will have to be too heavy 
to protect the smaller mains. 

Figure B shows a somewhat different arrangement which 
requires more wire and is more expensive in the beginning, 
but far more satisfactory and economical in operation. With 
the wires arranged as shown in the diagram the pressure at 
all the lamps will be nearly uniform. Even if the mains 
are designed for a considerable loss to the center of dis- 
tribution the dynamo may be made to compensate for this 
loss and keep the lamps burning properly. With the tree 
system, A, this is impossible ; the lamps at the first cut-out 
center will either be too bright or those at the last center 
too dim. 

Figure C shows a convertible three-wire system. Three- 
wire circuits may also be run as shown in Figures A and B, 
using three instead of two wires. 

In order to convert a three-wire system into a two-wire 
system the two outside wires are joined together. The mid- 
dle wire then forms one side of the system and the o'.itsid;^ 



118 



MODERN ELECTRICAL CONSTRUCTION. 




lSjT 




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Figure 62 



CONSTANT POTENTIAL SYSTEMS. 119 

wires the other. The middle wire must carry as much cur- 
rent as both outside wires combined and should have a carry- 
ing capacity equal to them. It should be remembered that a 
wire containing simply twice as many circular mils does not 
fulfil this requirement as is shown in the table on page — 
which must be consulted in selecting wires. 

In three-wire systems the middle or neutral wire is merely 
a balancing wire and normally carries very little or no current, 
but it is very important that it remain intact. If for instance 
in Figure D the branch circuit a has twelve lights burning 
while there are also 12 lights burning on b, the current will 
pass from the positive wire through the lower fuse to a, 
through the twelve lights in a back to the middle fuse, thence 
through the 12 lights in b to the upper fuse and negative wire, 
the two sets of lamps burning in series. If now the lamps in 
b are switched off the current from a can no longer pass 
through them and instead returns through the middle fuse to 
the neutral wire. If only six lights in b are burning, while 
12 are burning in a, the current of 6 lights will return over the 
negative wire and the other six in a will return over the 
neutral wire. Should the neutral wire be broken or its fuse 
blown there would be no return path on it for the extra cur- 
rent, and consequently the current passing through the twelve 
lights in a would be forced through the six lights in b, caus- 
ing them to burn with excessive brilliancy and to break in a 
very short time. Should a short circuit occur, say on circuit 
b, with the neutral wire intact, it would merely blow a fuse, 
but if the main neutral fuse were out it would bring 220 volts 
on circuit a and speedily cause damage to the lamps. Thus 
it will be seen that it is of great importance to fuse the neu- 
tral wire so that it will not easily blow out. The cut-out 
shown in Figure D is not approved because it does not pro- 
vide independent double fused branch circuits. The style of 
wiring shown in connection with it was formerly much in 
vcrr.:c bi't is not now much used. 



120 



MODERN ELECTRICAL CONSTRUCTION. 



Figure C shows a system of wiring quite often used. A 
set of heavy mains are run from the service or dynamo to the 
top floor and taps taken off at each floor. These mains do 
not change size at each floor, but are continuous for their en- 
tire length. While this method has some of the objections of 
the tree system in regards to voltage, still the faults of the 
tree system are greatly reduced to the much smaller losses 
in the mains between the upper floors or those farthest from 
the dynamo. 

Figure 63 shows the method of fusing main switch and 
branch circuits. The switch itself will require a fuse to pro- 
tect it although it need not be right at the switch. 

It often becomes necessary to reinforce a set of mains, 
especially for motors which have become overloaded, by run- 
ning another wire in parallel with the old as indicated in 
Figures 64 and 65. Two separate and distinct ways of ar- 




Tf F 





Fig. 63 Fig. 64 Fig. 65 Fig. 66 

ranging them are shown and it depends upon the conditions 
as to which is preferable. If the wires are small or run in 
places where they are liable to be broken, the plan shown in 
Figure 64 is the better. Here each wire is properly fused and 
if one breaks the other carries the whole load until its fuse 



CONSTANT POTENTIAL SYSTEMS. 121 

melts. If the wires, as often happens, are much overfused, 
the breaking of one wire would force the, other to carry 
the whole current and become overheated. If the arrange- 
ment were as in Figure 65 the unbroken wire would carry the 
current indefinitely and soon become overheated. On the 
other hand, if both wires are large and the run is short the 
fuses arranged as in Figure 64 may, through poor contacts, 
prevent one or the other of the wires from obtaining its 
full share of the current. The fuse making poor contact 
would force a much greater share of current through the 
other wire. In most cases the better plan would be to ar- 
range the wires as in Figure 65. If the current supplied is 
for lights the branch cut-outs can be separated and each set 
of mains allowed to supply a certain part of them, when 
each set should be made independent. For sizes of wires to 
be used for reinforcing, see Tables. 

With the three-wire system where a larger motor load 
and a few lights are run the lights are often fused as shown 
in Figure 66, a small wire being run for the neutral, this 
smaller wire, of course, being properly fused at the main cut- 
out. Plug cut-outs of the type shown in this figure often 
have the metal parts projecting above the porcelain; they 
should be connected so that the metal parts which project are 
dead when the plugs are removed. This will prevent many 
short circuits on disconnected cut-outs. 

Figure 67 shows the method of converting a two-wire 
system into a three-wire system with one extra wire to run. 
This extra wire will very likely not need to be as large as the 
other wires are, because the three-v/ire system requires only 
one-half as much current and it should, therefore, be used as 
the neutral. This arrangement will secure the full benefit of 
all the copper in the old wires (which are probably much larger 
than necessary) and will operate at a very small loss. 

Figure 68 shows a straight three-wire system changed to 



122 



MODERN ELECTRICAL CONSTRUCTION. 



a two-wire system, one extra wire run for it. If the three 
wires are of the proper capacity the addition of the fourth 
wire as in the figure will make it correct for two-wire sys- 




Figure 67 



Figure 



Figure 69 



tems, the mains feeding the upper and lower groups being, of 
course, properly fused where they start. 

In Figure 69 the cut-outs are so connected that all branch 
wires leaving the cut-out box at either side are of the same 
polarity. This is often useful where many wires are to be run 
close together. 

c. Must be in plain sight, or enclosed in an approved 
cabinet (see No. 54), and readily accessible. They must not 
be placed in the canopies or shells of fixtures. 

The ordinary porcelain link fuse cut-out will not be ap- 
proved. Link fuses may be used only when mounted on slate 
or marble bases conforming- to No. 52 and must be enclosed 
in dust-tight, fireproofed cabinets, except on switchboards 
located well away from combustible material, as in the ordi- 
nary engine and dynamo room and where these conditions will 
be maintained. 



CONSTANT POTENTIAL SYSTEMS. 123 

While it is required that cut-out cabinets be accessible there 
is also danger in making them too accessible, for such cabi- 
nets are very often used for storage of paper or cotton waste. 
It would seem that about eight feet above the floor is the 
most desirable height to place them or the cabinet may be 
arranged with a slanting bottom which will make it impossible 
to store anything in it. It is also well to arrange the cut-out 
cabinet away from inflammable material, for long experience 
has shown that doors are nearly always left open. Especially 
is this the case when switches are in the same cabinets with 
the cut-outs. 

d. Must be so placed that no set of incandescent lamps 
requiring more than 660 watts, whether grouped on one fixture 
or on several fixtures or pendants, will be dependent upon one 
cut-out. Special permission may be given in writing by the 
Inspection Department having jurisdiction for departure from 
this rule in the case of large chandeliers, stage borders and 
illuminated signs. 

The above rule shall also apply to motors when more 
than one is dependent on a single cut-out. 

The idea is to have a small fuse to protect the lamp 
socket and the small wire used for fixtures, pendants, etc. 
It also lessens the chances of extinguishing a large number 
of lights if a short circuit occurs. 

"On open work in large mills approved link fused ro- 
settes may be used at a voltage of not over 125 and approved 
enclosed fused rosettes at a voltage of not over 250, the fuse 
in the rosettes not to exceed 3 amperes, and a fuse of over 25 
amperes must not be used in the branch circuit." 

All branches or "taps" from a three-wire Edison system 
must be run as two-wire circuits. 

e. The rated capacity of fuses must not exceed the allow- 
able carrying capacity of the wire as given in No. 16. Circuit- 
breakers must not be set more than 30 per cent above the al- 
lowable carrying capacity of the wire, unless a fusible cut-out 
is also installed in the circuit. 

A 16 c. p. incandescent lamp is usually estimated at 55 
watts and consequently the number of lamps allowed on one 
circuit is usually twelve, whether 110 or 220 volts are used. 



124 MODERN ELECTRICAL CONSTRUCTION. 

If voltages lower than 110 are used the current required by^ 
twelve 55 watts lamps will be too great, and fewer lamps 
should be used per circuit. Although a number of small fan 
motors may be run on one circuit each motor should be pro- 
vided with a switch ; as a rule such a switch is on the motor. 

22. Switches. 

(See No. I'j, and for construction, No 51). 

a. Must be placed on all service wires, either overhead or 
underground, in a readily accessible place, as near as possible 
to the point where the wires enter the building and arranged 
to cut off the entire current. 

Service cut-out and switch must be arranged to cut off 
current from all devices including meters. 

In risks having private plants the yard wires running 
from building to building are not generally considered as ser- 
vice wires, so that switches would not be required in each 
building if there are other switches conveniently located on 
the mains or if the generators are near at hand. 

In overhead construction the best plan is to locate the 
switch at either front or rear of JDuilding so that wires may 
lead to it direct from pole. Avoid running wires on sides of 
building where it is likely that other buildings may be erected. 
In underground construction, where the space under sidewalk 
and basement is not occupied, it is advisable to place a cut-out 
where wires enter the building from street and to locate the 
service switch in a more accessible place. 

Although the rules do not call for switch to be installed in 
each separate building in the case of large plants, still it is 
often advisable to install them, for in case of trouble it is nec- 
essary that the current can be immediately shut off. A switch 
is also useful , in cases of trouble on the wiring, to allow of 
repairing. 

h. Must always be placed in dry, accessible places, and be 
grouped as far as possible. Knife switches must be so placed 
that gravity will tend to open rather than close them. 



CONSTANT POTENTIAL SYSTEMS. 



125 



When possible, switches should be so wired that blades 
will be "dead" when switch is open. 

If knife switches are used in rooms where combustible 
flying's would be likely to accumulate around them, they 
should be enclosed in dust-tight cabinets. (See note under 
No. 17 b.) Even in rooms where there are no combustible 
materials it is better to put all knife switches in cabinets, in 
order to lessen the danger of accidental short circuits being 
made across their exposed metal parts by careless workmen. 

Up to 250 volts and thirty amperes, approved indicating 
snap switches are advised in preference to knife switches 
on lighting circuits about the workrooms. 

To comply with this rule will ordinarily bring the fuses 
of knife switches directly under the handle of switch. If there 
happens to be a short circuit on the wires when switch is closed 
the fuses will blow instantly and very likely burn the operator's 
hand. In connection with such switches cartridge fuses should 
be used or the switches, especially the larger ones, closed by 




Figure 70 Figure 71 

pushing them in with a stick. The danger from opening a 
switch is much less. 

Figure 70 shows a switch arranged to comply with all three 
points of this rule, the feed wires coming from below. This 
requires that incoming and outgoing wires pass e-ach other. 
In this case, the wires pass each other behind the switch base, 



126 



MODERN ELECTRICAL CONSTRUCTION. 



they being encased in flexible tubing. A side view is also given 
in Figure 71. Instead of passing behind the switch the wires 
may, of course, run around one side to the top, the other wires 
around the other side to the bottom. 

Figure 71 illustrates a cabinet so arranged that the switch 
within can be opened or closed without opening the cabinet. 
The cover Is hingea at the top, and slotted in the center, which 
leaves room for the lever by which the switch is worked to 
adjust itself so it will always be out of the way. A switch 
which is often used may as well be left without a cover as with 
one, for the door must be opened or closed every time the 
switch is used, and the cabinet will always be found open. 
Figure 71 will answer where only protection against acci- 
dental contacts is required. 

c. Must not be single pole when the circuits which they 
control supply devices which require over 660 watts of energy, 
or when the difference of potential is over 300 volts. 

This rule allows the use of single pole switches on circuits 
of 660 watts, 6 amperes at 110 vots, or 3 amperes at 220 volts, 
which corresponds roughly to twelve 16 cp. lamps. In systems 
that are not grounded a single pole switch will answer fairly 




^mtmtm 



Figure 72 

well if large enough. It will readily open the circuit and it 
offers no opportunities for short circuits, as do double pole 
switches. Where, however, three wire systems with grounded 
neutrals are used double-pole switches are preferable, for by 
reference to Figure 72 one can readily see that if the neutral 



CONSTANT POTENTIAL SYSTEMS. 127 

or middle wire is grounded (which is equivalent to being in 
connection with gas piping) and another ground should come 
on to the wiring say at • o, the single-pole switch, S, would 
not control the lights at all. The current would flow from the 
positive wire to the top fuse, through the twelve lights to 
ground a, through the ground to the neutral or middle wire 
and back to the dynamo, regardless of whether the switch is 
on or off. Also, a man working at the lights could easily 
make a short-circuit by bringing the wires into contact with 
the gas piping even if the switch were turned off. When 
single-pole switches are used in connection with such circuits 
they should never be placed in the neutral wire as in the dia- 
gram. If the switch S were placed in the top wire these 
troubles would be avoided. Often times, however, switches 
are connected before the circuits are run into cut-outs and an 
attempt to place single-pole switches on a certain wire requires 
considerable care, which many wirem^en v/ill not take. In the 
case of only two wires from a central, three-wire, station being 
run into a building, the neutral wire is not known until meters 
are set and instructions would, therefore, have to be left for 
meter men which would often be disregarded, so that in all 
cases on three-wire grounded systems double-pole switches are 
preferable. 

d. Where flush switches are used, whether with conduit 
systems or not, the switches must be enclosed in boxes con- 
structed of iron or steel. No push buttons for bells, gas- 
lighting circuits, or the like shall be placed in the same wall 
plate with switches controlling electric light or power wiring. 

This requires an approved box in addition to the porce- 
lain enclosure of the switch. 

e. Where possible, at all switch or fixture outlets, a ^-inch 
block must be fastened between studs or floor timbers flush 
with the back of lathing to hold tubes, and to support switches 
or fixtures. When this cannot be done, wooden base blocks, 
not less than ^-inch in thickness, securely screwed to lathing, 



128 



MODERN ELECTRICAL CONSTRUCTION. 



must be provided for switches, and also for fixtures which are 
not attached to gas pipes or conduit tubing. 

Figure IZ shows concealed wiring back of lathing leading 
to a double-pole flush switch. The board fastened between 
studdings must be cut out to admit the box of switch and the 





Figure 73 



Figure 74 



size of this box should be known when wires are put in. The 
board should not rest hard against the lathing, but leave a 
little space for plaster to work in behind the lath. Loom is put 
on all wires at outlets and must extend back to the nearest 
knob. 

Figure 74 shows two methods of fastening snap switches 
by means of wooden blocks first fastened to the plaster. One 
block is cut out so as to bring all wires under the switch and 
entirely conceal them. The opening in block to admit wires 
and bushings should be oblong, so as to leave room on two 
sides for the screws with which the switch is to be fastened. 
On the other block the wires and bushing are brought through 
close to the outer edge of switch base. By careful workman- 
ship a neat job can be done in this way. As most snap 
switches cross conductors, that is, connect points a and h, if 



CONSTANT POTENTIAL SYSTEMS. 



129 



from the nature of the case it becomes necessary to run any of 
the wires close together these two wires may be run that way, 
for they can never be of opposite polarity. 



23. Electric Heaters. 

a. Must be placed in a safe situation, isolated from inflam- 
mable materials, and be treated as sources of heat. 

h. Must each have a cut-out and an indicating switch 
(see No. 17 a). 

c. The attachments of feed wires to the heaters must be in 
plain sight, easily accessible, and protected from interference, 
accidental or otherwise. 

d. The flexible conductors for portable apparatus, such as 
irons, etc., must have an approved insulating covering (see 
No. 45^). 

e. Must each be provided with name-plate, giving the 
maker's name and the normal capacity in volts and amperes. 



i 



O* 
O^ 




Figure 75 

Stationary heaters should be treated like stoves which 
might become overheated at any time. 

Portable heaters, such as flatirons, have this danger, that 
if left standing with the current on they in time accumulate 
heat enough to char combustible material and to finally set 
it on fire. 

It is often desirable to connect in multiple with the heat- 
ers, an incandescent lamp of low candle power, as it shows 
at a glance whether or not the switch is open, and tends to 
prevent its being left closed through oversight. 



130 MODERN ELECTRICAL CONSTRUCTION. 

In Figure 75 is given a diagram of a heater circuit with a 
4 cp. lamp in circuit. Where there are many irons in use, as in 
some tailoring establishments, it is advisable to run them all 
from one set of mains with a main switch convenient to exit 
door and have this switch opened whenever the irons are not 
in use. The individual switch at each iron should be located 
as near as possible to each iron. Cords feeding irons or cloth 
cutting machines are often installed as shown, insulators are 
strung on a tight wire and the cord tied to them. This allows 
considerable latitude in moving the iron. 



LOW POTENTIAL SYSTEMS. 



131 



Low-Potential Systems. 

550 Volts or Less. 

Any circuit attached to any machine, or combination of ma- 
chines, which develops a difference of potential between 
any tivo zuires, of over ten volts and less than 550 volts, 
shall be considered as a low-potential circuit, and as com- 
ing under this class, unless an approved transforming de- 
vice is used, zvhich cuts the diiference of potential down to 
ten volts or less. The primary circuit not to exceed a 
potential of 3,500 volts. 

Before Pressure is raised above 300 volts on any previously- 
existing* system of wiring-, the whole must be strictly hroug-ht 
up to all of the requirements of the rules at date. 



24. Wires. 



GENERAL RULES. 



{See also Nos. 14, 15 and 16.) 

a. Must "be so arrang"ed that under no circumstances will 
there be a difference of potential of over 300 volts between any 
bare metal parts in any distributing" switch or cut-out cabinet, 
or ecLuivalent center of distribution. 

This rule, as far as it applies to pressures higher than 300 

volts, contemplates a 3-wire system on which, instead of the 



\3=nj> ^ 



!l |a=03:> '- 




Figure 76 
customary 110 volts on each side of the neutral, 220 volts are 
used, making a pressure of 440 volts between the two outside 



132 



MODERN ELECTRICAL CONSTRUCTION. 



The ordinary 110-220 volt, 3-wire S3^stem will require to be 
changed at cut-out centers as shown in Figure 76, where it 
will be seen a difference of potential greater than 220 volts can- 
not be found within any cut-out box, or at any switch or cut- 
out. 

Special attention should be given to the balancing of the 
load with this arrangement of wiring and both sides of the 
system should be brought into every room or hall requiring 



\ \ \ \ \ \ I I 




Figure 77 

more than one circuit. False ideas of economy should not 
induce one to arrange large groups of lamps on one side of 
the system in order to save a few cut-out boxes. 

b. Must not be laid in plaster, cement, or similar finish, 
and must never be fastened with staples. 



LOW POTENTIAL SYSTEMS. 133 

c. Must not be fished for any great distance, and only in 
places where the inspector can satisfy himself that the rules 
have been complied with. 

Figure 77 illustrates a very common combination of "fish" 
and "moulding" work. Moulding is used to bring the wires 
from the floor to the ceiling and along the ceiling to a point 
opposite the outlet and parallel with the joists. From this 
point to the fixture the wires can then be readily fished. 

The connection between the fish and moulding work should 
be made as shown at the right, where ihe moulding is cut cut 
so as to admit the loom. It is better, even, to have the loom 
show to some extent than to have the wire come in contact 
with the plaster, as will very likely be the case if the loom is 
not fully brought through. 

d. Twin wires must never be used, except in conduits, or 
where flexible conductors are necessary. 

Flexible conductors are in general considered necessary 
only with pendant sockets, certain styles of adjustable brack- 
ets, portable lamps, motors and stage plugs, or heating ap- 
paratus. 

c. Must be protected on side walls from mechanical injury. 
When crossing floor timbers in cellars, or in rooms where they 
might be exposed to injury, wires must be attached by their 
insulating supports to the under side of a wooden strip, not 
less than one-half inch in thickness, and not less than three 
inches in width. Instead of the running boards, guard strips 
on each side of and close to the wires will be accepted. These 
strips to be not less than seven-eighths of an inch in thickness, 
and at least as high as the insulators. 

Suitable protection on side walls may be secured by a sub- 
stantial boxing, retaining- an air space of one inch around the 
conductors, closed at the top (the wires passing through bushed 
holes), and extending not less than five feet from the floor; or 
by an iron-armored or metal-slieathed insulating conduit suf- 
ficiently strong to withstand the strain to which it will be sub- 
jected, and with the ends protected by the lining or by special 
insulating bushings, so as to prevent the possibility of cutting 



134 



MODERN ELECTRICAL CONSTRUCTION. 



the wire insulation; or by plain metal pipe, lined with approved 
flexible tubing, which must extend from the nsulator next 
below the pipe to the one next above it. 

If metal conduits or iron pipes are used to protect wires car- 
rying alternating currents, the two or more wires of each cir* 
cuit must be placed in the same conduit, as troublesome induc- 
tion offects and heating of the pipe might otherwise result; and 
the insulation of each wire xnust be reinforced by approved flex- 
ible tubing extending from the insulator next below tlie pipe to 
the one next above it This should also be done in direct-cur- 
rent wiring if there is any possibility of alternating current 
ever being used on the system. 

For high-voltage work, or in damp places, the wooden boxing 
may be preferable, because of the precautions which would be 
necessary to secure proper insulation if the pipe were used. 
With these exceptions, however, iron pipe is considered prefer- 
able to the wooden boxing, and its use is strongly urged. It 
is especially suitable for the protection of wires near belts, pul- 
leys, etc. 

f. When run in unfinished attics, or in proximity to water 
tanks or pipes, will be considered as exposed to moisture. 



:^V^^^\\\\V\\\\\\\\\x\\u\\\M \ M I I I ,llf /f ' / A// / / J /. >f nrf /////// /^ 







Figure 78 



Figure 78 illustrates the meaning of the rule in regard to 
wires run along low ceilings. 

Figure 79 gives the dimensions necessary for boxing wires 
on side walls. At the right, the sidewall protection consists 
of conduit; a junction box with the lower side knocked out is 
used to enclose bushings. When the cover is screwed on the 
wires are completely enclosed. 



LOW POTENTIAL SYSTEMS. 



135 



SPECIAL RULES. 

For Open Work. 

In dry places. 

g. Must have an approved rubber or "slow-burning weath- 
erproof" insulation (see Nos. 41 and 42.) 

A "slow-burning weatherproof" covering is considered good 
enough where the wires are entirely on insulating supports. 
Its main object is to prevent the copper conductors from com- 
ing accidentally into contact with each other or anything else. 

Most of this wire as it is now made with the weather-proof 
braid on the outside, becomes sticky when exposed to the tem- 




Figure 79 



perature found in most mill rooms in summer. This is objec- 
tionable, especially in linty places, as dust and flyings readily 
adhere to the wires, making it difficult to keep them clear. 
Under these conditions, the "sweeping-down" process generally 
results in loosening and deranging the wires in a short time. 
The weatherproof insulation is also very combustible, and 



136 



MODERN ELECTRICAL CONSTRUCTION. 



when on the outside might allow fire to spread along the wires, 
especially if there were a number of wires near together, as 
stated in the note to No 2 b For these reasons it is considered 
preferable to place the weatherproof insulation next to the con- 
ductor, and the slow-burning braids on the outside. Tlie outer 
surface should then be finished hard and smooth, similar to 
that on the old so-called "underwriter" wire A wire insulated 
in this manner is not open to the objections noted above, and 
can also be more readily drawn into flexible tubing where the 
iron pipe construction described in the note to Section e is used. 
h. Must be rigidly supported on non-combustible, non- 
absorptive insulators, which will separate the wires from each 
other and from the surface wired over in accordance with the 
following table : 

Voltage. Distance from Distance between 

Surface. Wires. 

to 300 % inch 21/2 inch 

301 to 550 1 inch 4 inch 

Rigid supporting requires under ordinary conditions, where 
wiring along fiat surfaces, supports at least every four and 
one-half feet. If the wires are liable to be disturbed, the dis- 
tance between supports should be shortened. In buildings of 
mill construction, mains of No. 8 B. & S. gage wire or over, 
where not liable to be disturbed, may be separated about six 
inches, and run from timber to timber, not breaking around, 
and may be supported at each timber only. 

This rule will not be interpreted to forbid the placing of the 
neutral of an Edison three-wire system in the center of a three- 
wire cleat where the difference of potential between the outside 
wires is not over 300 volts, provided the outside wires are sep- 
arated two and one-half inches. 

Figure 80 shows different methods of running wires in 
buildings of mill construction. If the method shown at a is 



T 



Figure 80 



used, a few insulators should be placed here and there and the 
wires tied to them to prevent sagging. The arrangements 
shown at h and c are suitable for small wires on high ceilings. 



LOW POTENTIAL SYSTEMS. 137 

The methods shown at d and c are sometimes used where 
there is no danger of interference. With long spans, supports 
as shown at / may be used. 

In damp places, or buildings specially sitbjeef to moisture or 
to acid or other funics liable to injure the wires or their 
insulation. 

i. Must have an approved insulating covering. 

For protection against water, rubber insulation must be 
used. For protection against corrosive vapors, either weath- 
erproof or rubber insulation must be used (See Nos 41 and 44.) 

y. Must be, rigidly supported on non-combustible, non-ab- 
sorptive insulators, which separate the wire at least one inch 
from the surface wired over, and must be kept apart at least 
two and one-half inches for voltages up to 300, and four inches 
for higher voltages. 

Rigid supporting requires under ordinary con'ditions, where 
wiring over flat surfaces, supports at least every four and one- 
half feet. If the wires are liable to be disturbed, the distance 
between supports should be shortened. In buildings of mill 
construction, mains of No. 8 B. & S. gage wire or over, where 
not liable to be disturbed, may be separated about six inches, 
and run from timber to timber, not breaking around, and may 
be supported at each timber only. 

k. (Stricken out.) 

In damp places the wires are often run on the under side 
of an inverted trough as shown in Figure 81. The main point 
of usefulness of such a trough lies in the fact that it prevents 
drippings from wetting the wires and insulators. Condensa- 
tion will, however, keep insulators and wires wet nevertheless. 

The trough, to be useful, should be put together with many 
screws, the butting edges of the boards having been first 
painted with a waterproof paint, with which, when finished, the 
whole trough is also painted inside and out. 

Notwithstanding the rule given above, it would seem far 
better where practicable to use petticoat insulators and keep 
them much farther apart, even, if in order to do so a larger 
wire would be required. Each insulator, when wet, allows 
some current to leak over its surface and, therefore, the 



138 



MODERN ELECTRICAL CONSTRUCTION. 



fewer we have the better so long as there is no danger of break- 
ing wires. If spHces are necessary in wet places they should 
be made quite a distance from insulators ; the insulation of a 
splice being always weaker than that of the unbroken wire. 
Care should also be taken that the insulation of wires is not 
damaged through tying. 

Weather proof sockets are required by the rule and are 





Figure 81 

best in such places when not subject to much handling. As 
these are, however, easily broken, brass shell sockets are often 
used. These are thoroughly covered with tape and compound 
so as to exclude all moisture and are very durable. 

For Moulding Work. 

/. Must have an approved rubber insulating covering (see 
No. 41). 

m. Must never be placed in moulding in concealed or 
damp places, or where the difference of potential between any 
two wires in the same moulding is over 300 volts. 

As a rule, moulding should not be placed directly against 
a brick wall, as the wall is likely to "sweat" and thus introduce 
moisture back of the moulding. 

Figure 82 shows the dimensions of approved moulding. 
Figure 83 shows the proper method of making a tap joint 



LOW POTENTIAL SYSTEMS. 



139 



in moulding. This method brings the capping between the two 
wires of opposite polarity. Wires should never be crossed be- 
low the capping. If the exposed wire in Figure 83 is objec- 
tionable, part of the back of moulding may be cut out, or the 





Figure 82 



Figure 83 

wall back of the moulding may be gouged out as shown in Fig- 
ure 84. This method must, however, never be used with other 
than walls or partitions of hardwood. 

Figure 85 shows proper method of tapping flexible cord to 





Figure 86 



Fig. 84 Figure 85 

wires in moulding. The whole cord should never be taken 
out of one hole in capping. There is always some chance of 
abrasion and joints are often poorly covered, so that there is 
always mere likelihood of short circuits at this point. 



140 



MODERN ELECTRICAL CONSTRUCTION. 



Figure 86 shows how moulding should be fastened to tile 
ceiling. When toggle bolts are used, the nut should always be 
put on outside of capping (unless a very small one is used, or 





Figure 87 Figure 88 

more than ordinary care is exercised). Many wiremen are 
careless and cut away the middle tongue too much, giving the 
nut a chance to work itself diagonally across it, so as to come 
in contact with both wires and, in time perhaps, cause short 
circuits. Although toggle bolts are mostly used, screws have 
been successfully used in tile. It is only necessary to first 
drill a hole of just the proper size for the screw to be used. 

A very rough, quick way of making a square turn with 
moulding is shown in Figure 87. One piece is cut entirely 
off along the line a; the pieces are then joined as shown and 




Figure 89 

the capping hides the botch work. Such work will not be 
passed by inspectors if noticed. The proper way of fitting 
moulding is shown' in Figure 88. 



LOW POTENTIAL SYSTEMS. 141 

Figure 89 shows methods of running round corners. The 
saw cuts, a, b, c, etc., should be made with a fine saw and for 
short bends require to be close together. Bending is facilitated 
by wetting the moulding and if, before the moulding is put in 
place, the saw cuts are filled with glue, it will greatly add to 
the durability of the job. Screws or nails used in fastening 
the capping should pass through the moulding into the wall to 
get a firm hold. 

For Conduit Work. 

n. Must have an approved rubber insulating covering 
(see No. 47). 

0. Must not be drawn in until all mechanical work on the 
building has been, as far as possible, completed. 

p. Must, for alternating systems, have the two or more 
wires of a circuit drawn in the same conduit. 

It is advised that this be done for direct-current systems 
also, so that they may be changed to alternating systems at any 
time, induction troubles preventing such a change if the wires 
are in separate conduits. 

"The same conduit must never contain circuits of different 
systems, but may contain two or more circuits of the same 
system." 

If a single wire carrying alternating currents of electricity 
were run in iron pipe, there would be a very large drop in 
voltage. This drop is due to the fact that all currents while 
changing in strength generate a counter E. M. F. in their sur- 
roundings. This is particularly strong when the wires are sur- 
rounded by, or very close to, iron. If both wires are run in 
the same pipe, the current in one wire neutralizes that of the 
other and there is no trouble. 

For Concealed "Knob and Tube" Work. 

q. Must have an approved rubber insulating covering (see 
No. 41). 

r. Must be rigidly supported on non-combustible, non-ab- 



142 



MODERN ELECTRICAL CONSTRUCTION. 



sorptive insulators which separate the wire at least one inch 
from the surface wired over. Must be kept at least ten inches 
apart, and, when possible, should be run singly on separate 
timbers or studdings. Must be separated from contact with 
the walls, floor timbers and partitions through which they may 
pass by non-combustible, non-absorptive insulating tubes, such 
as glass or porcelain. 

Rig-id supporting requires under ordinary conditions, where 
wiring- along- flat surfaces, supports at least every four and one- 
half feet. If the wires are liable to be disturbed, the distance 
between supports should be shortened. 

s. "When, in a concealed knob and tube system, it is im- 




• Figure 90 

practicable to place any circuit on non-combustible supports 
of glass or porcelain, approved metal conduit, or approved 
armored cable must be used (see No. 24 t) except that if the 
difference of potential between the wires is not over 300 volts, 
and if the wires are not exposed to moisture, they may be 



LOW POTENTIAL SYSTEMS. 143 

fished on the loop system, if separately encased throughout in 
continuous lengths of approved flexible tubing." 

An illustration of wiring on the "loop" system is shown in 
Figure 90. This system makes it unnecessary to have any 
concealed joints or splices. The amount of wire required is 
somewhat in excess of that required for tap systems, but this 
is often balanced by a saving in labor. Sometimes, however, 
the labor is also in excess of that required for tap systems. 
The main advantage of the system is that all joints and splices 
are always accessible. The figure also shows mixed "knob 
and tube" work and "conduit" work. Along the walls behind 
the furring strips there is seldom sufficient space to admit of 
knob and tube work and conduit must be used. 

f. "Mixed concealed knob and tube work as provided for 
in No. 24 s, must comply with requirements of No. 24 n to p, and 
No. 25, when conduit is used, and with requirements of No. 
24 A, when armored cable is used." 

«. Must at all outlets, except where conduit is used, be 
protected by approved flexible insulating tubing, extending in 
continuous lengths from the last porcelain support to at least 
one inch beyond the outlet. In the case of combination fix- 
tures the tubes must extend at least flush with outer end of 
gas cap. 

Figure 91 Is drawn to illustrate "fish work." Fish work is 
used in finished buildings, mostly, and is often very tedious 
and expensive. Hours are sometimes spent before wires can 
be brought through and often the effort is an entire failure. 
In combination work, as shown in Figure 77, there is usually 
little trouble, as there is the whole span between joists to run 
wires in. An effort to fish at right angles to the joists (when 
there are strips under joists) is more difficult, but often suc- 
cessful if the distance is not too great. 

When there are two men the usual method of fishing is :. 
One man takes a wire sufficiently long to reach from one open- 
ing to the other, and, after bending a small hook on one end 



144 



MODERN ELECTRICAL CONSTRUCTION. 



in such a way that it will not catch easily on obstructions, 
pushes this end into one opening and, by tvv^isting and working 
backward and forward, gradually forces it toward the other 
opening. At this opening his helper is stationed with a short 
wire, also provided with a hook, with which he must seek to 
catch the other wire when it comes near his opening. When 
the two wires come in contact, the larger one is drawn out and 
the conducting wires (encased in approved flexible tubing) 
are fastened to it and drawn through. The tubing should 
always be put on the wires before drawing in. If it is put on 



■U.!.M»^-^-.JEk.xy^.!:,^^-^y^H^t'»(((te.J^^...>^t->-./;/.; 



)&»itoi:^i. ^X>ja|:^l^-S-gg 




Figure 91 

later there is much temptation to leave it as indicated at the 
right of the figure at a. This trick is quite common, but is 
very easily detected by inspectors ; the wire at either end can 
easily be pushed in without pushing out at the other, as it 
would if the tubing were continuous. If the tubing has been 
taped to the wires this will be impossible, but either one of the 
tubings can still be moved without moving the other, which 
would be impossible in a job properly done. The tubing must 
consist of one piece, and there must be only one wire in each 
tubing. 



LOW POTENTIAL SYSTEMS. 145 

If one man is alone on a fish job, a handful of small wire 
is pushed into one opening in a manner which will allow it 
to spread out considerably. When the fish wire from the 
other opening comes in contact with it, it will indicate it by 
moving this wire, which can be seen by that left hanging out. 
A small fish wire is then used to draw out the long one. If the 
two openings are in different rooms and not visible, one from 
the other, a bell and battery can be used, as shown in the 
drawing, if there are no wire lath. 

When wires are to be entirely concealed it is nearly always 
necessary to find a way through headers, timbers, etc. ; this 
can hardly be done without cutting holes in plaster. A method 
doing as little damage as any is shown at the top in Figure 91. 
A hole is bored through the 2X4, which will allow the wire, 
when job is finished, to continue downward as shown by dotted 
lines, 1 and 2, Such turns are seldom ever used with electric 
light wires on account of their size ; they are more practicable 
with bell or telephone wires. 

Where it is desired to keep wires from showing in a parlor, 
for instance, they can be fished from an adjoining room, as 
indicated by dotted line 3, where the wires are run down 
partition in moulding in closet and then through to switch, 
which is in the same room with the lights. Before under- 
taking a job of fish work it is well to look the whole building 
over carefully. There are often false walls along chimneys, 
especially at both sides of mantels, in which wires can be 
easily run from basement to attic. 

Often it may be necessary to remove baseboards in order 
to find room for wires. When removing such boards never 
attempt to drive nails out, always break them off; if driven 
out they will usually split off parts of the board. 

Soft wood floors can easily be taken up when necessary. 
Use a broad thin chisel and cut away the tongue on each side 



14 J MODERN ELECTRICAL CONSTRUCTION. 

of the board to be taken up; the board can then be readily 
taken up. With double floors or with tightly laid hardwood 
floors, it is better to cut pockets in ceiling below. 

For Fixture Work. 

V. Must have an approved rubber insulating covering (see 
No. 46), and be not less in size than No. 18 B. & S. gage. 

w. Supply conductors, and especially the splices to fixture 
wires, must be kept clear of the grounded part of gas pipes, 
and, where shells or outlet boxes are used, they must be made 
sufficiently large to allow the fulfillment of this requirement. 

X. Must, when fixtures are wired outside, be so secured 
as not to be cut or abraided by the pressure of the fastenings 
or motion of the fixture. 

y. Under no circumstances must there be a difference of 
potential of more than 300 volts between wires contained in or 
attached to the same fixture. 

Rule 24 A. New Rule. Armored Cables. 

{For Construction Rules sec No. 48.) 

a. Must be continuous from outlet to outlet or to junction 
boxes, and the armor of the cable must properly enter and be 
secured to all fittings. 

Note — In case of underground service connections and main 
runs, this involves running- such armored cable continuously 
into a main cut-out cabinet or gutter surrounding the panel 
board, as the case may be. (See No. 54.) 

b. Must be equipped at every outlet with an approved out- 
let box or plate, as required iii conduit work. (See No. 49 
/ to o.) 

Note. — Outlet plates must not be used where it is practicable 
to install outlet boxes. 

In buildings already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 
tion Department having jurisdiction, provided the armored 
cable is firmly and rigidly secured in place. 

c. Must have the metal armor of the cable permanently 
and effectively grounded. 



LOW POTENTIAL SYSTEMS. 147 

Note — It is essential that the metal armor of such sj'stems 
be joined so as to afford electrical conductivity sufficient to 
allow the largest fuse or circuit breaker in the circuit to operate 
before a dangerous rise in temperature in the system can occur. 
Armor of cables rfnd gas pipes must be securely fastened in 
metal outlet boxes so as to secure good electrical connection. 
Where boxes used for centers of distribution do not afford good 
electrical connection, the armor of the cables must be joined 
around them by suitable bond wires. Where sections of ar- 
mored cable are installed without being fastened to the metal 
structure of buildings or grounded metal piping, they must 
be bonded together and joined to a permanent and efficient 
ground connection. 

d. When installed in so-called fireproof buildings in course 
of construction or afterwards if concealed, or where it is ex- 
posed to the weather, or in damp places such as breweries, 
stables, etc., the cable must have a lead covering at least 1/32 
of an inch in thickness placed between the outer braid of the 
conductors and the steel armor. 

e. Where entering junction boxes at all other outlets, etc., 
must be provided with approved terminal fittings which will 
protect the insulation of the conductors from abrasion, unless 
such junction or outlet boxes are specially designed and ap- 
proved for use with the cable. 

f. Junction boxes must always be installed in such a man- 
ner as to be accessible. 

g. For alternating current systems must have the two or 
more conductors of the cable enclosed in one metal armor. 

25. Interior Conduits. 

{See also Nos. 2471 to p, and 4g.) 

The object of a tube or conduit is to facilitate the insertion 
or extraction of the conductors and to protect them from me- 
chanical injury. Tubes or conduits are to be considered merely 
as raceways, and are not to be relied upon for insulation be- 
tween wire and wire, or between the wire and the ground. 

The installation of wires in conduit not only affords the 

wires protection from mechanical injury, but also reduces the 

liability of a short circuit or ground on the wires producing 

an arc, which would set fire to the surrounding material; the 

conduit being generally of sufficient thickness to blow a fuse 

before the arc can burn through the metal of the pipe. For 



148 MODERN ELECTRICAL CONSTRUCTION. 

this reason the wires should be entirely encased in metal 
throughout, both in the conduit and at all outlets. Another 
advantage derived from the use of iron conduit is the facility 
with which wires can be extracted and replaced in case a 
fault develops on any of them. The saving which this may 
mean in cases where the installation of new wires would 
necessitate the destruction of costly decorations can readily be 
seen. It must be remembered that the arc or burn produced 
by a short circuit or ground is proportional to the size of the 
fuse protecting the circuit. If a large fuse, say 30 amperes, is 
used to protect a branch circuit and a ground or short occurs 
on this circuit, the wire may become fused to the pipe so that 
it cannot easily be pulled out. This is one reason why fuses 
should be as small as practicable. More than six amperes is 
seldom used on branch circuits, so that no larger fuse than 
this should ordinarily be used. The installation of wires in 
iron conduit also reduces the liability of lightning discharges 
entering a building as the pipe surrounding the wires offers 
great resistance to the passage of these sudden currents. 

Conduit is classed. under two general heads, lined and un- 
lined. In both classes of conduit the same thickness of metal 
is required. 

a. No conduit tube having an internal diameter of less 
than five eighths of an inch shall be used. Measurements to 
be taken inside of metal conduits. 

This rule favors lined conduit insomuch that it requires 
the same pipe for lined and unlined, and allows a lined con- 
duit of less than five-eighths of an inch in diameter. 

b. Must be continuous from outlet to outlet or to junc- 
tion boxes, and the conduit must properly enter, and be secured 
to all fittings. 

In case of underground service connections and main runs, 
this involves running each conduit continuously into a main 
cut-out cabinet or gutter surrounding the panel board, as the 
case may be (see No, 54.) 

When conduit is used every run of pipe must end in acces- 



LOW POTENTIAL SYSTEMS. 



149 



sible outlet boxes. This box may be a cutout center, switch 
outlet, jfixture outlet or a junction box. If a mixed form of 
wiring is used, where part of a circuit is run in conduit and 
the balance with some other form of construction, such as 
concealed knob and tube work, for instance, the conduit must 
in all cases enter the box and be firmly attached to it, as 
shown in Figure 92. Cases are sometimes found where the 
conduit is brought just to the box, but does not enter it, the 




K 



--iuYictlon box 



AotK -nvA*; 




f-'--l...Q 



Figure 92 

wires being extended through holes into the box. This method 
of wiring is obviously wrong; as a wireman is apt to find if 
he ever has occasion to replace wires in such a system. The 
same holds true of cutout centers. Here also every run of 
conduit must enter the box. The conduit should not simply 
be brought to the sides or the back of the cutout center and 
the wires then carried to the cutouts in flexible tubing, but 
every conduit should enter clear into the box so that when 
the work is completed there will be no exposed wiring. In 



150 



MODERN ELECTRICAL CONSTRUCTION. 



the case of main runs the conduit should enter the boxes and 
never be broken between the outlets. Sometimes it is neces- 
sary to install meters on the mains and the conduit is ended 
and the wires carried to the meters and then either extended 
in conduit or carried into the cutout center. This construc- 
tion should be avoided. If a meter is to be installed near a 
cutout center, the main conduit should be carried into the box 
and the necessary meter loops then brought out. In this way 




Figure 93 

the quantity of wire outside of conduits is reduced to a mini- 
mum. If a meter is to be installed in some location along the 
mains other than at the cutout center or service switch, a 
junction box should be provided and the meter loops brought 
out from that. This is shown in Figure 93, which also shows 
a cutout box as used with conduit systems. 

c. Must be first installed as a complete conduit system, 
without the conductors. 

As fast as the conduit is installed, the ends of the pipes 



LOW POTENTIAL SYSTEMS. 151 

should be closed, using paper or corks. This does away with 
the liability of plaster or other substances entering the pipes 
and causing trouble when the wires are to be pulled in. The 
conductors should not be pulled in until all the mechanical work 
on the building is, as far as possible, fi;iished. When a con- 
duit system is ready for the wires, the "pulling in" may be 
done in various ways. For short runs, all that is necessary is 
to shove the wires in at one opening until they come out at 
the other. If a run is too long to be inserted in this way, 
what is known as a "fish wire" can be used. The ordinary 
fish wire is a flat band of steel about 5/32 inch wide and 1/32 
inch thick. This wire can be forced through any ordinary 
length of pipe. Ordinary round steel wire of about No. 12 
or 14 B. & S. gauge can also be used for fish wire, although this 
is not as good as the fish wire above described. 

The end of the wire is first bent back so as to form a very 
small hook or eye ; this will enable it to slide easily over ob- 
structions in the pipe and also make it possible should it stick 
somewhere to engage it with another fish wire provided with 
a suitable hook and entered from the other end of the pipe. 
This is very often necessary in runs having many bends. The 
fish wire, having been pushed through the pipe, is now fastened 
to the copper wire by means of a strong hook and the copper 
wire pulled into the pipe. 

In pulling in the large size cables, it is often found advan- 
tageous to pull on the fish wire and at the same time push on 
the end of the cable entering the pipes. It is also well to 
remember that it is easier to pull down than to pull up, as, 
when pulling down, the weight of the cable assists. The use 
of soapstone facilitates the drawing in of the wires. The wire 
may either be covered with the powdered soapstone or the 
soapstone may be blown into the pipes. An elbow partly 
filled with soapstone is often found convenient for blowing the 
soapstone into the pipe, always blowing from the highest point. 



152 MODERN ELECTRICAL CONSTRUCTION. 

d. Must be equipped at every outlet with an approved out- 
let box or plate (see No. 49 I to o). 

Outlet plates must not be used where it is practicable to 
install outlet boxes. 

In building's already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 
tion Department having jurisdiction, providing the conduit ends 
are bushed and secured. 

The object of an outlet box is to hold the conduits firmly 
in place, to connect the various runs of conduit so that they 
form a continuous electrical path to the ground, and to afford 
a fireproof enclosure for the joints, switches, etc. Outlet 
boxes are made in various designs to meet the requirements 
of the work on which they are to be used. 

Where it is impossible to use an outlet box, an outlet plate 
can be used. These plates are fitted with set screws so that 
they hold the ends of the conduits firmly in position and make 
the metal of the system continuous. They do not afford a 
fireproof enclosure for the joints and for that reason should 
never be used when it is practicable to use an outlet box. If 
the conditions are such that neither an outlet box or plate can 
be used, special permission can be obtained from the Inspec- 
tion Department having jurisdiction to omit them. In this 
case the conduits should be bushed at the ends and the pipes 
should be bonded together. 

e. Metal conduits where they enter junction boxes, and at 
all other outlets, etc., must be provided with approved bushings 
fitted so as to protect wire from abrasion, except when such 
protection is obtained by the use of approved nipples, properly 
fitted in boxes or devices. 

When a piece of conduit is cut with a pipe cutter, a sharp 
edge is left on the inside. This edge, if left on, would soon 
cut into the insulation of the wires. It should be removed by 
means of a pipe reamer. The bushing can now be screwed on 
as shown in Figure 92, a locknut having first been screwed 



LOW POTENTIAL SYSTEMS. 153 

onto the pipe. The locknut and bushing are then screwed up 
so that they are tight and form a good connection. 

/. Must have the metal of the conduit permanently and 
effectually grounded. 

It is essential that the metal of conduit systems be joined 
so as to afford electrical conductivity sufficient to allow the 
largest fuse or circuit breaker in the circuit to operate before 
a dangerous rise in temperature in the conduit system can 
occur. Conduits and gas pipes must be securely fastened in 
metal cutlet boxes so as to secure good electrical connection. 
Where boxes used for centers of distribution do not afford 
good electrical connections, the conduits must be joined 
around them by suitable bond wires. Where sections of metal 
conduit are installed without being fastened to the metal struc- 
ture of buildings or grounded metal piping, they must be bonded 
together and joined to a permanent and efficient ground con- 
nection. 

That the metal in a conduit system should be permanently 
and effectually grounded is plainly evident when the hazards 
which are present with ungrounded or poorly grounded con- 
duit are recalled. Until recently very little attention has 
been given to the matter of properly grounding conduits, but 
with the increased use the necessity of so doing has become 
very apparent. If the bare wire of one side of a system comes 
in contact electrically with the iron pipe, and if there is a 
ground on the other side of the system (and there always is 
with 3-wire systems) the conduit becomes a conductor. If 
the conduit system is so installed that every piece is in good 
electrical connection and the entire system effectually grounded 
no harm will be done except the blowing of a fuse. Conduit is 
installed in all kinds of locations. It may be in contact with a 
gas pipe, lead pipe, or run in a damp floor, or it may be run 
exposed where a person could easily come in contact with it. 
The effects that might result from a conduit so run should the 
conduit become alive are readily seen. Suppose that in the 
first case the conduit crosses the gas pipe at right angles, the 
area of contact would be very small and the effect of the cur- 
rent in a livened conduit crossing this poor contact would 



154 MODERN ELECTRICAL CONSTRUCTION. 

result in burning a hole in the gas pipe and igniting the escap- 
ing gas. Again, suppose the conduit run in a damp floor 
should become alive; the damp wood work, being a conductor, 
would soon char and the charred part would then readily 
ignite. With a system which is grounded, an exposed piece 
of conduit will usually only be alive for a very short time 
during the blowing of the fuse. Even if it remains perma- 
nently alive, current will not flow from it to the surrounding 
material, but will take the easiest path to ground; which is 
along the conduit. On the ordinary branch circuits, the vari- 
ous runs of conduit are bonded together through the outlet 
boxes and, in connecting the conduits to these boxes, care must 
be taken that they make good contact. In order to do this, the 
conduit should enter at right angles to the box and the enamel 
should be scraped away from the box so that the locknut and 
bushing make good electrical connection. The same thing 
should be done where the conduit enters the cutout box. The 
metal of the cutout box will bond together the various branch 
conduits and the main conduit. The main conduit should now 
be connected to some good ground, such as a water or steam 
pipe or metal work of the building. Never carry the ground 
wire to a gas pipe. The various branch conduits should also 
be grounded wherever possible, at and on metal beams over 
which they cross and at every gas outlet. The reason of 
grounding the gas pipe thoroughly at the gas outlets is to be 
sure of a good ground. The gas pipe is necessarily in contact 
with the outlet box at this point and any poor contact which 
might cause arcing must be avoided. 

Strictly speaking, a conduit should be grounded with a wire 
equal to that used in the conduit. This can easily be done in 
the case of smaller circuits, but with the larger size mains it is 
a more difficult matter. No special device has as yet been 
designed for the ground wire connection, the usual practice 
being to take a number of good turns around the conduit and 



LOW POTENTIAL SYSTEMS. 155 

then solder the wire to the conduit and tape the joint. A 
better way would be to use a few T couplings on the system 
and to screw brass plugs to these and solder the ground wire 
to the plugs. Such couplings should be installed near outlets 
where they will not interfere much with "fishing." 

If the ground wire has to be run for any great distance, 
it should be installed as though it were at all times alive, and 
should be kept away from inflammable material. The method 
advised under 13 A for grounding wires should be used. 
Where a 3-wire system is used, the best ground obtainable is 
the neutral wire of the system. When a ground is made to 
the neutral wire, it should be made back of the fuses on the 
service switch; never make the connection with the neutral 
inside of the service switch. 

g. Junction boxes must always be installed in such a 
manner as to be accessible. 

h. All elbows or bends must be so made that the con- 
duit or lining of same will not be injured. The radius of the 
curve of the inner edge of any elbow not to be less than three 
and one-half inches. Must have not more than the equivalent 
of four quarter bends from outlet to outlet, the bends at the 
outlets not being counted. 

If more than four quarter bends are necessary, a junction 
box should be installed and the wires first pulled from one 
of the outlets to the junction box and then from the junction 
box to the other outlet. 

Several methods are in use for bending conduit. With the 
lined conduit elbows and bends of various shapes can be 
obtained already bent, and it is much more satisfactory to use 
these, as considerable care must be exercised in making bends 
in order to keep the inside lining from coming loose from 
the pipe and causing trouble when "pulling in." To prevent 
this a suitable spiral spring is sometimes inserted into the con- 
duit before bending. Plumbers working with lead pipe often 
use coarse sand to fill the pipe before bending. This is more 



156 MODERN ELECTRICAL CONSTRUCTION. 

particularly useful with special conduits such as brass tubing, 
which is sometimes used in showcase or window work and 
classed with fixtures. 

With unlined conduits the bending is a simple matter, 
although here also care must be taken to see that the conduit 
does not bend flat. In a good bend the pipe retains its circular 
form throughout the bend, while, if the bend is poorly made, 
the pipe will assume an oval shape, flattening somewhat at 
the bend. The smaller size conduits can be bent in a common 
vise. This is best accomplished by gripping the pipe in the 




Figure 94 

vise and making a small bend, then moving the pipe for a slight 
distance and bending again, and continuing until the desired 
shape is obtained. Another method which can be used on 
small pipes is shown at a in Figure 94, using a three or four 
foot length of gas pipe or conduit with an ordinary gas pipe T 
on the end. This is run over the conduit and gives sufficient 
leverage to make any bend. 

A simple device used for bending conduits is shown at 
b in Figure 94. This is constructed of metal, the wheel being 
grooved to fit the pipe. A similar device, minus the wheel 
and lever, may be made up of two blocks of wood firmly 
fastened to a work bench. The pipe can be bent around this 
by hand. 

For the larger size conduits, elbows can be obtained already 
bent. Connections between the various lengths of conduit are 



LOW POTENTIAL SYSTEMS. 157 

made with the ordinary gas-pipe couplings. When the conduit 
comes from the factory each length of pipe is provided with a 
coupling at one end. (This practice is now being discon- 
tinued, the couplings being left off.) This coupling should be 
removed and the end of the conduit reamed out. The reaming 
should always be done so that there is considerable metal left 
at the end of the pipe, and it should never be carried so far as 
to leave only a sharp edge. If a thread is to be cut, it is good 
practice to take a couple of turns with the reamer after this has 
been done. The coupling can then be screwed on. When 
making the connection, the pipes should be screwed into the 
coupling so that the ends just "butt." Do not attempt to screw 
them too tight, or, in all probability, the thread on the end 





Figure 95 

of the pipe will be turned in and close the opening. Figure 
95, a, shows how a connection should be made. If lined con- 
duit is not properly reamed and is screwed too tight, the 
opening is often entirely closed or forced inward, as shown 
at b. 

It is often necessary, especially in making changes in old 
installations, to fit pieces between two pipes, neither one of 
which can be turned so as to draw them together. In such 
cases a long thread is cut on one piece of the pipe and the 
coupling run back on it; when the pipes are butted together 
the coupling is run over the two pipes, thus connecting them. 
A locknut may be run upon either pipe and used to keep the 
coupling in place. 

In running conduits avoid as much as possible passing 
through bath-rooms and other places where plumbers are 
likely to run their piping. 



158 MODERN ELECTRICAL CONSTRUCTION. 

When practicable, conduits should be run so they will drain ; 
for instance, where crossing a room from one side bracket to 
another, it is better to run along ceiling than along the floor. 
Conduits will sometimes become quite moist inside from con- 
densation. Where there is any likelihood of this the ends may 
be sealed. 

26. Fixtures. 

(See also Nos. 22 e, 24 v to x.) 

a. Must when supported from the gas piping or any 
grounded metal work of a building be insulated from such 
piping or metal work by means of approved insulating joints 
(see No. 59) placed as close as possible to the ceiling. 

"Gas outlet pipes must be protected above the insulating 
joint by approved insulating tubing, and where outlet tubes 
are used they must be of sufficient length to extend below 
the insulating joint, and must be so secured that they will not 
be pushed back when the canopy is put in place 

"Where canopies are placed against plaster walls or ceilings 
in fireproof buildings, or against metal walls or ceilings, or 
plaster walls or ceilings on metallic lathing in any class of 
buildings, they must be thoroughly and permanently insulated 
from such walls or ceilings." 

Figure 96 shows insulating joints such as are used to insu- 
late fixtures from the gas piping of buildings. 

The object of an insulating joint is to prevent a "ground" 






Figure 96 

on one fixture from causing trouble on other fixtures. If, for 
instance, one fixture in a building were in contact with the 
positive wire of the system and another in contact with a nega- 
tive wire, and the two fixtures connected direct to the gas 



LOW POTENTIAL SYSTEMS. 



159 



piping, the two contacts or "grounds" would form a short cir- 
cuit; the current flowing from one pole along the gas piping to 
the other. This becomes impossible when the fixtures are 
insulated from the piping, or conducting parts of ceilings. 

Insulating joints are made in a variety of patterns. The 
one shown at a in Figure 96 is designed for use on a combina- 
tion gas and electric fixture, and is made to allow the gas to 
pass through. Other forms, such as h, can be used on conduit 
work to connect to the stub in the outlet box, or on a gas outlet 
where it is desired to use the electric light only. 

Insulating joints should be placed as close as possible to the 
ceiling, so that there will be a minimum of exposed pipe above 




Figure 97 

the joint. If the gas pipe has been left long so that the insu- 
lating joint comes some distance below the ceiling, it is a good 
plan to protect the pipe above the joint either by using a porce- 
lain tube which will fit over the pipe or by taping the pipe 
thoroughly. Flexible tubing is also sometimes used. See 
Figure 97. 

In connecting the fixture, care should be taken that the 
extra wire usually left for making the joint is twisted around 
the pipe below the insulating joint; never above. If the wires 
at the outlet have been properly run, as shown in Figure 97, 
the flexible tubing will extend to the bottom of the insulating 
joint. 



160 



MODERN ELECTRICAL CONSTRUCTION. 



When a straight electric fixture is to be installed on some 
grounded part of the building, a crowfoot, shown at c, Figure 
96, can be fastened to the metal work and the fixture then con- 
nected with the insulating joint. 

If the fixture is to be mounted on plaster, a hardwood 
block can be screwed to the wall or ceiling and a crowfoot 
screwed to this. The screws holding the crowfoot must not 
extend through the block. Such a case is illustrated at the 
right in Figure 97. 

Before the plastering is put on, a board should be fastened 
between the joists, so that tne wooden block may later be 
screwed to it. This is not absolutely necessary, as screws in 
lath will usually hold light fixtures. Heavy fixtures in old 




Figure 98 



buildings can best be hung as shown at h, in Figure 98. This 
method is also used for ceiling fan motors. These motors 
m.ust never be rigidly fastened, but should always be left free 
to swing and find their own centers. 

In connection with open or moulding work, the canopies 
should always be cut out, so that the loom or moulding may 
enter them. On no account should wires be allowed to rest 
on sharp edge of canopy. See a, Figure 98. 

Figure 98 illustrates at c how fixtures are fastened to tile 
ceilings, toggle bolts and a metal strip to which a piece of pipe 
is fastened being used. 



LOW POTENTIAL SYSTEMS. 161 

Fiber is often used for the ins,ulation of canopies from the 
ceiling. Figure 98 at d shows a bug insulator, which can be 
used for this purpose. A hole is drilled in the center of a 
small block of fiber, and it is then slotted lengthwise with a 
saw. A small dent is made in the upper edge of the canopy 
and the fiber blcck slipped on the edge, so that the small dent 
fits into the hole. If a hole is punched through the edge of 
the canopy, and a brass pin riveted in, a much better job is 
obtained. Short, thin strips of fiber, or a long strip riveted to 
the inside of the canopy and left to project about one-eighth 
inch, are often used. These being placed on the inside of the 
canopy are much more sightly than the bug insulators. When 
a wooden block is used to fasten the fixture to the wall, the 
block may be made large enough so tlfat the canopy will fit 
against it. The practice of fastening the canopy a short dis- 
tance from the ceiling does not comply with the rule. 

b. Must have all burs, or fins, removed before the con- 
ductors are drawn into the fixture. 

c. Must be tested for "contacts," between conductors and 
fixture, for "short circuits" and for ground connections before 
it is connected to its supply conductors. 

Fixtures are always made up of gas piping and their con- 
struction is, therefore, very similar to conduit work. 

Three tests should be made on each fixture before it is con- 
nected. If tests are not made until fixtures have been con- 
nected, it is often necessary to disconnect them again to de- 
termine whether a fault is in the fixture or in the wiring. 
Where there are several fixtures on one circuit and a short 
circuit should be discovered, it would also likely be necessary 
to disconnect several of them before the right one would be 
found. 

A test for short circuit may be made, first, by connecting 
the two w4res of a magneto to the two main wires at top of 
fixtures. If all sockets are properly connected and the wiring 



162 MODERN ELECTRICAL CONSTRUCTION, 

is clear, no ring will be obtained. If a ring is obtained, It 
indicates a short circuit. 

Without changing connections each socket may now be 
tested for connections. While one man is operating the mag- 
neto, another may insert a screw-driver, jack-knife, or piece of 
wire into each socket in turn, thus connecting the two termi- 
nals and causing a ring of the magneto. Failure to obtain a 
ring would indicate an open circuit, which must, of course, be 
remedied. 

The third test is made for "grounds." To make it, the two 
fixture wires are connected to one wire of the magneto and 
the other wire is connected to the metal of the fixture. 

It is best to connect this wire to the iron piping, and not to 
the lacquered brass ; the lacquer is often a very good insulator. 
If a ring is now obtained, it indicates that the insulation on a 
wire has been damaged, and that the bare wire is in contact 
with the fixture. This test can be made more thorough by 
working the accessible fixture wires back and forth during the 
test ; sometimes, a damaged portion of wire is not in contact 
with the metal of fixture while lying upon the floor, but may be 
brought in contact with it when hanging. 

Fixtures that have been connected to the circuit and pro- 
vided with insulating joints can be individually tested for 
"grounds," by connecting one wire of a magneto to the body 
of the fixture and the other, first to one, and then the other, 
of the circuit wires in the sockets. This test will detect a 
"ground" in a fixture without disconnecting it from the cir- 
cuit. 

In connecting sockets to fixtures, it is advisable to connect 
them so that all protruding parts, as keys or receptacles for 
lamps, be of the same polarity, that is, all connected to the 
same main wire. This also applies to reflectors, border lights 
for theaters, encased in metal, etc. This will not lessen the 
liability of such parts to "ground," but lessens the chances 



LOW POTENTIAL SYSTEMS. 163 

of short circuits very much. Many ''shorts" are brought about 
by the projecting brass lamp butts on fixtures being of opposite 
polarity. If they are of the same polarity, they will cause no 
trouble. 

Special fixtures for show windows, etc., are often made up 
as shown in Figure 99. The construction shown at the left is 
more compact and neat, but requires more care in installing 




Figure 99 



than the other, because of the edges of pipe in contact with 
the wires. If very long fixtures of this kind are installed, it is 
advisable to insert insulating joints as often as practicable, 
even if necessary to run wires around them. 

27. Sockets. 

(For construction rules, see No. 3^.) 

a. In rooms where inflammable gases rnay exist the incan- 
descent lamp and socket must be enclosed in a vapor-tight 
globe, and supported on a pipe-hanger, wired with approved 
rubber-covered wire (see No. 41) soldered directly to the 
circuit. 

In Figure 100, a shows a "vapor-tight" globe suspended on 
a pipe hanger, the construction of which complies with the 
requirements of this rule. If moisture is present it is well to 
seal the upper end of the pipe with compound. 



164 



MODERN ELECTRICAL CONSTRUCTION. 



h. In damp or wet places, or over specially inflammable 
stuff, waterproof sockets must be used. 

Waterproof sockets should be hung by separate, stranded, 
rubber-covered wires, not smaller than No. 14 B. & S. gage, 
which should preferably be twisted together when the pendant 
is over three feet long. These wires should be soldered direct 
to the circuit wires, but supported independently of them. 

Waterproof sockets are constructed entirely of porcelain 
and are not provided with keys, therefore the circuits to which 
they are connected must be controlled by switches. As a gen- 
eral rule these sockets are furnished with a short piece oi 




Figure 100 

stranded, rubber-covered wire extending through sealed holes 
in the top of the socket and the supporting wires are soldered 
to them. The method of suspending waterproof sockets varies 
with the conditions. Ordinarily, stranded rubber-covered 
wires of the proper length are suspended from single cleats as 
shown at h, in Figure 100, or, if the line knobs are large 
enough, the stranded wire may be supported from them. If 
the lamp is to be suspended only a short distance from the 



LOW POTENTIAL SYSTEMS. 165 

ceiling, where it will not be liable to be disturbed, it may be 
hung from two ordinary inch porcelain knobs, as shown in 
Figure 81. If cleats are used in a damp place for supporting 
the drop a half cleat must be provided back of the supporting 
cleat to give a one-inch separation, as required for wires in 
wet places. 

28. Flexible Cord. 

a. Must have an approved insulation and covering (see 
No. 45). 

b. Must not be used where the difference of potential 
between the two wires is over 300 volts. 

c. Must not be used as a support for clusters. 

d. Must not be used except for pendants, portable lamps 
or motors, and portable heating apparatus. 

The practice of making the pendants unnecessarily long and 
then looping them up with cord adjusters is strongly advised 
against. It offers a temptation to carry about lamps which are 
intended to hang freely in the air, and the cord adjusters wear 
off the insulation very rapidly. 

For all portable work, including those pendants which are 
liable to be moved about sufficiently to come in contact with 
surrounding objects, flexible wires and cables especially de- 
signed to withstand this severe service are on the market, and 
should be used. (See No. 45 f.) 

The standard socket is threaded for one-eighth-inch pipe, 
and if it is properly bushed, the reinforced flexible cord will 
not go into it, but this style of cord may be used with sockets 
threaded for three-eghths-inch pipe, and provided with sub- 
stantial insulating bushings. The cable to be supported inde- 
pendently of the overhead circuit by a single cleat, and the two 
conductors then separated and soldered to the overhead wires. 

The bulb of an incandescent lamp frequently becomes hot 
enough to ignite paper, cotton and similar readily ignitible 
materials, and in order to prevent it from coming in contact 
with such materials, as well as to protect it from breakage, 
every portable lamp should be surrounded with a substantial 
wire guard. 

Flexible cord should be used only for drop lights which 
hang free in the air, or for desk lights or fan motors, where 
the cord is so installed that it is not liable to injury. 

Cord adjusters should never be used where their use can 



166 MODERN ELECTRICAL CONSTRUCTION. 

be avoided and where they are installed should only be placed 
on lamps which will seldom need adjusting. The indis- 
criminate use of cord adjusters cannot be too strongly con- 
demned as the constant rubbing soon destroys the insulation. 
At c, Figure 100, shows a brass socket threaded for ^-inch 
pipe, and which is designed to be used with portable cord. 
Care should be taken in making up these sockets to see that 
the knot under the head of the socket has a good bearing 
surface so that it will not pull through the larger bushing, these 
portables being very apt to be jerked about. 

A lamp guard to be of any value should be sO/ constructed 
that the bulb of the lamp cannot come in contact with any- 
thing outside of the lamp guard ; it should also protect the 
lamp from any sudden jar. The design of the guard should 
be such that it can be firmly attached to the socket so it will 
not work loose and come in contact with the live butt of the 
lamp or projecting threaded portion of the socket. 

e. Must not be used in show windows. 

The great number of fires which have been caused by the 
use of flexible cord in show windows is sufficient argument 
against its use. Portable cord, or what is kown as "show 
window" cord, should be used. 

/. Must be protected by insulating bushings where the 
cord enters the socket. 

g. Must be so suspended that the entire weight of the 
socket and lamp will be borne by knots under the bushing 
in the socket, and above the point where the cord comes 
through the ceiling block or rosette, in order that the strain 
may be taken from the joints and binding screws. 

Special ceiling blocks or rosettes which facilitate the 
fastening of cords are on the market and should be used. In 
fastening the cord to sockets the end of the cord should be 
soldered. This does away with the liability of stray strands 
short circuiting on the shell of the socket and also affords a 



LOW POTENTIAL SYSTEMS. 



167 



better and stronger contact under the binding screws. This 
soldering is best done by dipping the ends of the cord in melted 
solder. If a blow torch is used the small wires are very easily 
overheated and the soldering may do more harm than good. 
It is also well to tape the ends of cords, leaving only just 
enough bare metal to go under the binding screws; the tape 
will hold the end of the braid and will confine any ends of wires 
which do not happen to come under the binding screws. 



29. Arc Lamps on Constant-Potential Circuits. 

a. Must have a cut-out (see No. 17 a) for each lamp or 
each series of lamps. 

The branch conductors should have a carrying capacity 
about 50 per cent, in excess of the normal current required by 
the lamp to provide for heavy current required when lamp is 
started or when carbons become stuck without overfusing the 
wires. 

Figure 101 at the left gives a diagram of a constant poten- 
tial arc circuit as generally used at present for enclosed arc 
lamps. Each arc lamp of this kind requires a pressure of 110 




Figure 101 

volts. A steadying resistance, R, is always placed in series 
with constant potential lamps, its object being to keep down 
the current while the lamp feeds. During the short time that 
the two carbons are together, the resistance of the lamp is so 
low that an enormous amount of current would flow were it 
not for this resistance. With most lamps this resistance is 



168 MODERN ELECTRICAL CONSTRUCTION. 

now installed in the liood. Since the rule requires a carrying 
capacity about 50 per cent in excess of the normal current for 
branch conductors, it would be well to provide this also for 
mains in such cases where groups of arc lamps are likely to be 
controlled by one switch and used together. 

Figure 101 at the right shows a diagram of wiring for open 
arc lamps. Two lamps are usually run in series on 110 volts 
together with a steadying resistance. An open arc does not 
work well with a pressure higher than about 45 volts. 

b. Must only be furnished with such resistance or regula- 
tors as are enclosed in non-combustible material, such resist- 
ances being treated as sources of heat. Incandescent lamps 
must not be used for this purpose. 

c. Must be supplied with globes and protected by spark 
arresters and wire netting around the globe, as in the case of 
series arc lamps (see Nos. 19 and 58). 

Outside arc lamps must be suspended at least eig-ht feet 
above sidewalks. Inside arc lamps must be placed out of reach 
or suitably protected. 

30. Economy Coils. 

a. Economy and compensator coils for arc lamps must be 
mounted on non-combustible, non-absorptive insulating sup- 
ports, such as glass or porcelain, allowing an air space of at 
least one inch between frame and support, and must in gen- 
eral be treated as sources of heat. 

31. Decorative Lighting Systems. 

a. Special permission may be given in writing by the 
Inspection Department having jurisdiction for the temporary 
installation of approved Systems of Decorative Lighting, pro- 
vided the difference of potential between the wires of any 
circuit shall not be over 150 volts and also provided that no 
group of lamps requiring more than 1,320 watts shall be de- 
pendent on one cut-out. 

No "System of Decorative Lighting" to be allowed under 
this rule which is not listed in the Supplement to the National 
Electrical Code containing list of approved fittings. 



LOW POTENTIAL SYSTEMS. 169 

b. Incandescent lamps connected in series must not be 
used for decorative purposes inside of buildings except by 
special permission in writing from the Inspection Department 
having jurisdiction. 

32. Car Wiring. 

a. Must always be run out of reach of the passengers, 
and must have an approved rubber insulating covering (see 
No. 41). 

33. Car Houses. 

a. The trolley wires must be securely supported on insu- 
lating hangers. 

b. The trolley hangers must be placed at such a distance 
apart that, in case of a break in the trolley wire, contact cannot 
be made with the floor. 

c. Must have a cut-out switch located at a proper place 
outside of the building, so that all trolley circuits in the build- 
ing can be cut out at one point, and line circuit-breakers must 
be installed, so that when this cut-out switch is open the trolley 
wire will be dead at all points within 100 feet of the building. 
The current must be cut out of the building whenever the 
latter is not in use or the road is not in operation. 

d. All lamps and stationary motors must be installed in 
such a way that one main switch can control the whole of each 
installation — lighting or power — independently of the main 
feeder switch. No portable incandescent lamps or twin wire 
will be allowed, except that portable incandescent lamps may 
be used in the pits, the circuit to be controlled by a switch 
placed outside of the pit, and the connections to be made by 
two approved rubber-covered flexible wires (see No. 41), 
properly protected against mechanical injury. 

. e. All wiring and apparatus must be installed in accord- 
ance with rules for constant-potential systems. 

f. Must not have any system of feeder distribution cen- 
tering in the building. 

g. The rails must be bonded at each joint with a con- 



170 MODERN ELECTRICAL CONSTRUCTION. 

diictor having a carrying capacity not less than that of a No. 2 
B. & S. gage annealed copper wire. 

h. Cars must not be left with tha trolley in electrical con- 
nection with the trolley wire. 

34. Lighting and Power from Railway Wires. 

a. Must not be permitted, under any pretence, in the same 
circuit with trolley wires with a ground return, except in 
railway cars, electric car houses and their power stations; nor 
shall the same dynamo he used for hoth purposes. 



HIGH-POTENTIAL SYSTEMS. 

550 TO 3,500 Volts. 

Any circuit attached to any machine or combination of ma- 
chines which develops a difference of potential, between 
any two wires, of over 550 volts and less than 3,300 volts, 
shall be considered as a high-potential circuit, and as 
coming under that class, unless an approved transforming 
device is used, which cuts the difference of potential down 
to 550 volts or less. 

35. Wires. 

(See also Nos. 14, 15 and 16.) 

a. Must have an approved rubber-insulating covering (see 
No. 41). 

b. Must be always in plain sight and never encased, except 
where required by the Inspection Department having juris- 
diction. 

c. Must be rigidly supported on glass or porcelain insula- 
tors, which raise the wire at least one inch from the surface 
wired over, and must be kept about eight inches apart. 

Rigid supporting- requires under ordinary conditions, where 
wiring along flat surfaces, supports at least about every four 
and one-half feet. If the wires are unusually liable to be 
disturbed, the distance between supports should be shortened. 

In buildings of mill construction, mains of No. 8 B. & S. 
gage or over, where not liable to be disturbed, may be separated 
about ten inches and run from timber to timber, not breaking 
around, and may be supported at each timber only. 



HIGH POTENTIAL SYSTEMS. 171 

d. Must be protected on side walls from mechanical 
injury by a substantial boxing, retaining an air space of one 
inch around the conductors, closed at the top (the wires 
passing through bushed holes) and extending not less than 
seven feet from the floor. When crossing floor timbers, in 
cellars, or in rooms where they might be exposed to injury, 
wires must be attached by their insulating supports to the 
under side of a wooden strip not less than one-half an inch in 
thickness. 

For general suggestions on protection, see note under 
No. 24 e. See also note under No. 18 e. 

36. Transformers. (When permitted inside buildings, see 

No. 13.) 

(For construction rules, see No. 62.) 
(See also Nos. 13 and 13 A.) 

Transformers must not be placed inside of buildings with- 
out special permission from the Inspection Department having 
jurisdiction. 

a. Must be located as near as possible to the point at 
which the primary wires enter the building. 

h. Must be placed in an enclosure constructed of fire- 
resisting material ; the enclosure to be used only for this pur- 
pose, and to be kept securely locked, and access to the same 
allowed only to responsible persons. 

c. Must be effectually insulated from the ground, and the 
enclosure in which they are placed must be practically air- 
tight, except that it must be thoroughly ventilated to the out- 
door air, if possible, through a chimney or flue. There should 
be at least six inches air space on all sides of the transformer. 

37. Series Lamps. 

a. No multiple series or series multiple system of light- 
ing will be approved. 

h. Must not, under any circumstances, be attached to gas 
fixtures. 



172 MODERN ELECTRICAL CONSTRUCTION. 

EXTRA-HIGH-POTENTIAL SYSTEMS. 

Over 3,500 Volts. 

Any circuit attached to any machine or combination of ma- 
chines which develops a diiference of potential, between 
any two wires, of over 3,500 volts, shall be considered as 
an extra-high-potential circuit, and as coming under that 
class, unless an approved transforming device is used, 
zuhich cuts the diiference of potential down to 3,500 volts 
or less. 

38. Primary Wires. 

a. Must not be brought into or over buildings, except 
power stations and sub-stations. 

39. Secondary Wires. 

a. Must be installed under rules for high-potential sys- 
tems when their immediate primary wires carry a current at a 
potential of over 3,500 volts, unless the primary wires are 
installed in accordance with the requirements as given in rule 
12 A or are entirely underground, within city, town and village 
limits. 



NOTICE— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class D. 

FITTINGS, MATERIALS AND DETAILS OF 
CONSTRUCTION. 



ALL SYSTEMS AND VOLTAGES. 
Insulated Wires— Rules 40 to 48 

40. General Rules. 

a. Copper for insulated conductors must never vary in 
diameter so as to be more than two one-thousandths of an inch 
less than the specified size. 

h. Wires and cables of all kinds designed to meet the 
following specifications must be plainly tagged or marked as 
follows : 

1. The maximum voltage at which the wire is designed to 
be used. 

2. The words "National Electrical Code Standard." 

3. Name of the manufacturing company and, if desired, 
trade name of the wire. 

4. Month and year when manufactured. 

It is recommended that all wires complying with these 
specifications be provided with a distinctive marking- on the 
insulation or braid which will serve to identify them at any 
time. 

4L Rubber-Covered Wire. 

a. Copper for conductors must be thoroughly tinned. 



174 MODERN ELECTRICAL CONSTRUCTION. 

b. Must be of rubber or other approved substance, and of 
a thickness not less than that given in the following table: 

B. & S. Gage. Thickness. 

18 to 16 1-32 inch. 

15 to S 3-64 " 

7 to 2 1-16 " 

1 to 0000 5-64 " 

CircularMils. 

250,000 to 500,000 3-32 " 

500,000 to 1.000,000 7-64 " 

Over 1,000,000 1-8 " 

Measurements of insulating- wall are to be made at the 
thinnest portion of the dielectric. 

c. The completed coverings must show an insulation 
resistance of at least 100 megohms per mile during thirty days' 
immersion in water at seventy degrees Fahrenheit. 

d. Each foot of the completed covering must show a 
dielectric strength sufficient to resist throughout five minutes 
the application of an electro-motive force of 3,000 volts per 
one sixty-fourth of an inch thickness of insulation under the 
following conditions : 

The source of alternating electro-motive force shall be a 
transformer of at least one kilowatt capacity. The application 
of the electro-motive force shall first be made at 4,000 volts 
for five minutes and then the voltage increased by steps of not 
over 3,000 volts, each held for five minutes, until the rupture 
of the insulation occurs. The tests for dielectric strength shall 
be made on a sample of wire which has been immersed m 
water for seventy-two hours. One foot of the wire under 
test is to be submerged in a conducting liquid held in a metal 
trough, one of the transformer terminals being connected to 
the copper of the wire and the other to the metal of the trough. 

Insulations for Voltages between 600 and 3,500 

c. The thickness of the insulating wall must not be less 
than that given in the following table : 

B. & S. Gage. Thickness. 

14 to 1 3-32 inch. 

to 0000 3-32 inch, covered by tape or braid. 

Circular Mils. 

250,000 to 500,000 3-32 inch, covered by tape or braid. 

Over 500,000 1-8 inch, covered by tape or braid. 



FITTINGS, MATERIALS, ETC 175 

f. The requirements as t o insulation and breai<-down 
resistance for wires for low-potential systems shall apply, with 
the exception that an insulation resistance of not less than 300 
megohms per mile shall be required. 

Insulation for Voltage over 3,500. 

g. Wire for arc-light circuits exceeding 3,500 volts poten- 
tial must have an insulating wall not less than three-sixteenths 
of an inch in thickness, and shall withstand a breakdown test 
of at least 30,000 volts and have an insulation of at least 500 
megohms per mile. 

The tests on this wire to be made under the same condi- 
tions as for low-potential wires. 

Specifications for insulations for alternating currents ex • 
ceeding- 3,500 volts have been considered, but on account of the 
somewhat complex conditions in such work, it has so far been 
deemed inexpedient to specify general insulations for this use. 

Protecting Braid. 

h. All of the above insulations must be protected by a 
substantial braided covering, property saturated with a pre- 
servative compound. This covering must be sufficiently strong 
to withstand all the abrasion likely to be met with in practice, 

Figure 103 

and sufficiently elastic to permit all wires smaller than No. 7 
B. & S. gage to be bent around a cylinder with twice the 
diameter of wire, without injury to the braid. 

42. Slow-burning Weatherproof Wire. 

(See Figure 103.) 

a. The insulation must consist of two coatings, one to be 
fireproof in character and the other to be weatherproof. The 
fireproof coating must be on the outside and must comprise 



176 MODERN ELECTRICAL CONSTRUCTION. 

about six-tenths of the total thickness of the wall. The com- 
pleted covering must be of a thickness not less than that given 
in the following table : 

B. & S. Gage. Thickness. 

14 to 8 3-64 inch. 

7 to 2 1-16 " 

1 to 0000 5-64 " 

Circular Mils. 

250.000 to 500.000 3-32 " 

500,000 to 1.000,000 7-64 " 

Over 1,000,000 1-8 " 

Measurements of insulating wall are to be made at the 
thinnest portion of the dielectric. 

This wire is not as burnable as "weatherproof," nor as sub- 
ject to softening under heat. It is not suitable for outside 
work. 

b. The fireproof coating shall be of the same kind as that 
required for "slow-burning wire," and must be finished with a 
hard, smooth surface if it is on the outside. 

c. The weatherproof coating shall consist of a stout braid, 
applied and treated as required for "weatherproof wire," and 
must be thoroughly slicked down if it is on the outside. 

43. Slow-burning Wire. 

a. "The insulation must consist of layers of cotton or 
other thread, all the interstices of which must be filled with the 
fireproofing compound, or of material having equivalent fire 



Figure 104 

resisting and insulating properties. The outer layer must 
be braided and specially designed to withstand abrasion. The 
thickness of insulation must not be less than that required for 
slow-burning weatherproof wire and the outer surface must be 
finished smooth and hard." 

"The solid constituent of the fireproofing compound must 
not be susceptible to moisture, and must not burn even when 
ground in an oxidizable oil, making a compound which, while 
proof against fire and moisture, at the same time has consider- 



. FITTINGS, MATERIALS, ETC. 177 

able elasticity, and which when dry will suffer no change at a 
temperature of 250° P.. and which will not burn at even a 
higher temperature. 

44. Weatherproof Wire. 

(Sec Figure 104.) 

a. The insulating covering shall consist of at least three 
braids, all of which must be thoroughly saturated with a dense 
moisture-proof compound, applied in such a manner as to 
drive any atmospheric moisture from the cotton braiding, 
thereby securing a covering to a great degree waterproof and 
of high insulating power. This compound must retain its 
elasticity at deg. Fahr. and must not drip at 160 deg. Fahr. 
The thickness of insulation must not be less than that required 
for "slow-burning weatherproof wire," and the outer surface 
must be thoroughly slicked down. 

This wire is for use outdoors, where moisture is certain and 
where fireproof qualities are not necessary. 

45. Flexible Cord. 

(For installation rules, see A^o. 28.) 

a. Must be made of stranded copper conductors, each 
strand to be not larger than No. 26 or smaller than No. 30 



Figure 105 

B. & S. gage, and each stranded conductor must be covered 
by an approved insulation and protected from mechanical 
injury by a tough, braided outer covering. 

For Pendant Lamps. 

(See Figure 105.) 

In this class is to be included all flexible cord which, under 
usual conditions, hangs freely in air, and which is not likely 
to be moved sufficiently to ccme in contact with surrounding 
objects. 

It should be noted that pendant lamps provided with long 
cords, so that they can be carried about or hung over nails or 



178 MODERN ELECTRICAL CONSTRUCTION. 

on machinery, etc., are not included in this class, even though 
they are usually allowed to hang- freely in air. 

b. Each stranded conductor must have a carrying capacity- 
equivalent to not less than a No. 18 B. & S. gage wire. 

c. The covering of each stranded conductor must be made 
up as follows : 

1. A tight, close wind of fine cotton. 

2. The insulation proper, which shall be waterproof. 

3. An outer cover of silk or cotton. 

The wind of cotton tends to prevent a broken strand punc- 
turing the insulation and causing a short circuit. It also keeps 
the rubber from corroding the copper. 

d. The insulation must be solid, at least one thirty-second 
of an inch thick, and must show an insulation resistance of 
fifty megohms per mile throughout two weeks' immersion in 
water at 70 degrees Fahrenheit, and stand the tests prescribed 
for low-tension wires as far as they apply. 

e. The outer protecting braiding should be so put on and 
sealed in place that when cut it will not fray out, and where 
cotton is used, it should be impregnated with a flameproof 
paint, which will not have an injurious effect on the insulation. 

For Portables. 

{See Figure io6.) 

In this class is included all cord used on portable lamps, 
small portable motors, or any device which is liable to be 
carried about. 

f. Flexible cord for portable use must meet all of the 
requirements for flexible cord "for pendant lamps," both as to 



Figure 106 

construction and thickness of insulation, and in addition must 
have a tough braided cover over the whole. There must also 
be an extra layer of rubber between the outer cover and the 
flexible cord, and in most places the outer cover must be sat- 
urated with a moisture-proof compound, thoroughly slicked 
down, as required for "weatherproof wire" in No. 44. In 



FITTINGS, MATERIALS, ETC. 179 

offices, dwellings or in similar places where the appearance is 
an essential feature, a silk cover may be substituted for the 
weatherproof braid. 

For Portable Heating Purposes. 

(See Figure 107.) 

g. Must be made up as follows : 

1. A tight, close wind of fine cotton. 

2. A thin la3'er of rubber or other cementing material 
about one one-hundreth of an inch thick. 




Figure 107 

3. • A layer of asbestos insulation at least three sixty- 
fourths of an inch thick. 

4. A stout braid of cotton. 

5. An outer reinforcing cover especially designed to with- 
stand abrasion. 

This cord is in no sense waterproof, the thin layer of rubber 
being- intended merely to serve as a seal to help hold in place 
the fine cotton and asbestos, and it should be put on in such a 
way as will accomplish this. 

46. Fixture Wire. 

(See Figure 108.) 

(For installation rules, see No. 24 v to y.) 

a. May be made of solid or stranded conductors, with no 
strands smaller than No. 30 B. & S. gage, and must hav^e a 
carrying capacity not less than that of a No. 18 B. viz: S. gage 
wire. 

b. Solid conductors must be thoroughly tinned. If a 
stranded conductor is used, it must be covered by a tight, close 
wind of fine cotton. 

c. Must have a solid rubber insulation of a thickness not 
less than one thirty-second of an inch for Nos. 18 to 16 B. & S. 



180 MODERN ELECTRICAL CONSTRUCTION. 

gage, and three sixty-fourths of an inch for Nos. 14 to 8 B. & 
S. gage, except that in arms of fixtures not exceeding twenty- 
four inches in length and used to supply not more than one 
sixteen-candle-power lamp or its equivalent, which are so con- 

Figure 108 

structed as to render impracticable the use of a wire with one 
thirty-second of an inch thickness of rubber insulation, a 
thickness of one sixty-fourth of an inch will be permitted. 

d. Must be protected with a covering at least one sixty- 
fourth of an inch in thickness, sufficiently tenacious to with- 
stand the abrasion of being pulled into the fixture, and suf- 
ficiently elastic to permit the wire to be bent around a cylinder 
with twice the diameter of the wire without injury to the braid. 

e. Must successfully withstand the tests specified In Nos. 
41 c and 41 d. 

47. Conduit Wire. 

(For installation rules, see No. 24 n to p.) 

a. Single wire for lined conduits must comply with, the 
requirements of No. 41 (Figure 109). For unlined conduits 
it must comply with the same requirements — except that tape 



Figure 109 Figure 110 Figure 111 

may be substituted for braid — and in addition there must be 
a second outer fibrous covering, at least one thirty-second of 
an inch in thickness and sufficiently tenacious to withstand the 
abrasion of being hauled through the metal conduit. (Figures 
110 and 111). 

b. For twin or duplex wires In lined conduit, each con- 
ductor must comply with the requirements of No. 41 — except 
that tape may be substituted for braid on the separate con- 



FITTINGS, MATERIALS, ETC. 



181 



ductors — and must have a substantial braid covering the whole. 
For unlined conduit, each conductor must comply with require- 
ments of No. 41 — except that tape may be substituted for braid 
— and in addition must have a braid covering the whole, at 
least one thirty-second of an inch in thickness and sufficiently 
tenacious to withstand the abrasion of being hauled through 
the metal conduit (Figure 112). 

c. For concentric wife, the inner conductor must comply 
with the requirements of No. 41 — except that tape may be 
substituted for braid — and there must be outside of the outer 
conductor the same insulation as on the inner, the whole to be 




Figure 112 Figure 113 

covered with a substantial braid, which for unlined conduits 
must be at least one thirty-second of an inch in thickness, and 
sufficiently tenacious to withstand the abrasion of being hauled 
through the metal conduit (Figure 113). 

The braid or tape required around each conductor in duplex, 
twin and concentric cables is to hold the rubber insulation in 
place and prevent jamming and flattening. 



48. Armored Cable. 

(Sec Figure 114.) 

a. The armor of such cables must have at least as great 
strength to resist penetration of nails, etc., as is required for 




Figure 114 



metal conduits (see No. 49 b), and its thickness must not be 
less than that specified in the following table : 



182 



MODERN ELECTRICAL CONSTRUCTION. 



Nominal 


Actual 


Actual 




Internal 


Internal 


External 


Thickness 


Diameter. 


Diameter. 


Diameter 


of Wall. 


Inches. 


Inches. 


Inches. 


Inches. 


i/« 


.27 


.40 


.06 


% 


.36 


.54 


.08 




.49 


.67 


.09 


3/ 


.62 


.84 


.10 


.82 


1.05 


.11 


1 ^ 


1.04 


1.31 


.13 


\t 


1.38 


1.66 


.14 


1.61 


1.90 


.14 


2 


2.06 


2.37 


.15 


21/2 


2.46 


2.87 


.20 


3 


3.06 


3.50 


.21 


31/2 


3.54 


4.00 


.22 


4 


4.02 


4.50 


.23 


41/2 


4.50 


5.00 


.24 


5 


5.04 


5.56 


.25 


6 


6.06 


6.62 


.28 



An allowance of two one-hundredths of an inch for variation 
in manufacturing- and loss of thickness by cleaning will be 
permitted. 

b. The conductors in same, single wire or twin conductors, 
must have an insulating covering as required by No. 41 ; if 
any filler is used to secure a round exterior, it must be impreg- 
nated with a moisture repellent, and the whole bunch of con- 
ductors and fillers must have a separate exterior covering. 

49. Interior Conduits. 

(For installation rules, see Nos. 24 n to p and 25.) 

a. Each length of conduit, whether lined or unlined, must 
have the maker's name or initials stamped in the metal or 
attached thereto in a satisfactory manner, so that inspectors 
can readily see the same. 

The use of paper stickers or tags cannot be considered satis- 
factory methods of marliing, as they are readily loosened and 
lost oft in the ordinary handling of the conduit. 

Metal Conduits with Lining of Insulating Material. 

{See Figure 115.) 

b. The metal covering or pipe must be at least as strong 
as the ordinary commercial forms of gas pipe of the same 
size, and its thickness must be not less than that of standard 
gas pipe as specified in the table given in No. 48. 

c. Must not be seriously affected externally by burning 



FITTINGS, MATERIALS, ETC. 183 

out a wire inside the tube when the iron pipe is connected to 
one side of the circuit. 

d. Must have the insulating lining firmly secured to the 
pipe. 

e. The insulating lining must not crack or break when a 
length of the conduit is uniformly bent at temperature of 212 
degrees Fahrenheit to an angle of ninety degrees, with a curve 




Figure 115 

having a radius of fifteen inches, for pipes of one inch and less, 
and fifteen times the diameter of pi'pe for larger sizes. 

f. The insulating lining must not soften injuriously at a 
temperature below 212 degrees Fahrenheit and must leave 
water in which it is boiled practically neutral. 

g. The insulating lining must be at least one thirty-second 
of an inch in thickness. The materials of which it is com- 
posed must be of such a nature as will not have a deteriorating 
effect on the insulation of the conductor and be sufficiently 
tough and tenacious to withstand the abrasion test of drawing 
long lengths of conductors in and out of same. 

h. The insulating lining must net be mechanically weak 
after three days' submersion in water, and when removed 
from the pipe entire, must not absorb more than ten per cent 
of its weight of water during 100 hours of submersion. 

i. All elbows or bends must be so made that the con- 
duit or lining of same will not be injured. The radius of the 
curve of the inner edge of any elbow must not be less than 
three and one-half inches. 



Unlined Metal Conduits. 

(See Figure ii6.) 

j. Plain iron or steel pipes of thickness and strengths 
equal to those specified for lined conduits in No. 49 h may be 



184 



MODERN ELECTRICAL CONSTRUCTION. 



used as conduits, provided their interior surfaces are smooth 
and free from burs. In order to prevent oxidation, the pipe 
must be galvanized, or the interior surfaces coated or en- 




Figure 116 

ameled with some substance w^hich will not soften so as to 
become sticky and prevent the wire from being withdrawn 
from the pipe. 

k. All elbows or bends must be so made that the conduit 
will not be injured. The radius of the curve of the inner edge 
of any elbow not to be less than three and one-half inches. 



Outlet Boxes. 

{Sec Figure 117.) 

I. Must be of pressed steel having a wall thickness not 
less than .081 in. (No. 12 B. & S. gage) or of cast metal hav- 




Figure 117 

ing a wall thickness not less than 0.128 in. (No. 8 B. & S. 
gage). 

m. Must be well galvanized, enameled or otherwise coated, 
inside and out, to pi event oxidation. 



FITTINGS, MATERIALS, ETC. 185 

n. Inlet holes must be effectually closed when not in 
use by metal which will afford protection substantially equiv- 
alent to that of the walls of the box. 

0. Must be plainly marked where it will be seen when 
installed with the name or trade mark of the manufacturer. 

p. Boxes used with lined conduit must comply with the 
foregoing and in addition must have a tough and tenacious 
insulating lining firmly secured in position. 

50. Wooden Mouldings. 

(See Figure ii8.) 
{For zuiring rules, see No. 24, I and m.) 

a. Must have, both outside and inside, at least two coats 
of waterproof material, or be impregnated with a moisture 
repellent. 

h. Must be made in two pieces, a backing and a capping, 
and must afford suitable protection from abrasion. Must be 
so constructed as to thoroughly encase the wire and provide 




vi^ 



STAItSARD UOUUIIIIG. 



I*- -*| 




Figure 118 



a one-half inch tongue between the conductors and a solid 
backing, which, under grooves, shall not be less than three- 
eighths of an inch in thickness. 

It is recommended that only hardwood moulding be used. 

50A. Tubes and Bushings. 

{See Figure 118.) 
a. Construction. — Must be made straight and free from 



186 



MODERN ELECTRICAL CONSTRUCTION. 



checks or rough projections, with ends smooth and rounded 
to facihtate the drawing in of the wire and prevent abrasion 
of its covering. 

b. Material and Test. — Must be made of non-combustible 
insulating material, which, when broken and submerged for 
100 hours in pure water at 70 degrees Fahrenheit, will not 
absorb over one-half of one per cent of its weight. 

c. Marking. — Must have the name, initials, or trade mark 
of the manufacturer stamped in the ware. 

d. Sizes. — Dimensions of walls and heads must be at 
least as great as those given in the following table : 



Diameter 

of 

Hole. 

Inches. 

5/16 

% 

1/2 

k 

1% 

2 

21/4 
21/2 

An allowance of one-sixty-fourth of an inch for variation 
in manufacturing will be permitted, except in the thickness of 
the wall. 



External 


Thick*- 


External 


Length 


Diameter. 


ness of 


Diameter 


of 




Wall. 


of Head. 


Head. 


Inches. 


Inches. 


Inches. 


Inches. 


9/16 


1/8 


13/16 


1/2 


11/16 


5/32 


15/16 


1/2 


13/16 


5/32 


1 3/16 


1/2 


15/16 


5/32 


1 5/16 




1 3/16 


7/32 


1 11/16 


% 


1 7/16 


7/32 


1 15/16 


% 


1 13/16 


9/32 


2 5/16 


1 


2 3/16 


11/32 


2 11/16 


2 9/16 


13/32 


3 1/16 


2 15/16 


15/32 


3 7/16 


% 


3 5/16 


17/32 


3 13/16 


1 


3-11/16 


19/32 


4 3/16 


1 



SOB. Cleats. 



(See Figure 118.) 



a. Construction. — Must hold the wire firmly in place 
without injury to its covering. 

Sharp edges which may cut the wire should be avoided. 

b. Supports. — Bearing points on the surface must be 
made by ridges or rings about the holes for supporting screws, 
in order to avoid cracking and breaking when screwed tight. 

c. Material and Test. — Must be made of non-combustible 
insulating material, which, when broken and submerged for 



FITTINGS, MATERIALS, ETC, 187 

100 hours in pure water at 70 degrees Fahrenheit, will not 
absorb over one-half of one per cent of its weight. 

d. Marking. — Must have the name, initials or trademark 
of the riianufacturer stamped in the ware. 

e. Sizes. — Must conform to the spacings given in the fol- 
lowing table : — 





Distance from Wire 


Distance between 


oltag-e. 


to Surface. 


Wires. 


0-300 


V:^ inch. 


2V2 inches. 



This rule will not be interpreted to forbid the placing of the 
neutral of an Edison three-wire system in the center of the 
three- wire cleat wliere the difference of potential between the 
outside wires is not over SCO volts, provided the outside wires 
are separated two and. one^half inches. 

50 C. Flexible Tubing. 

(See Figure 119.) 

The following specifications are designed to cover the 
construction of flexible tubes for fished work, loop system and 
for mechanical protection to wires where not exposed to 
moisture. 

Tubes complying with these requirements must not be used 
for a conduit system of wiring. 

a. Must be constructed to meet the following require- 
ments : 

Must have a sufficiently smooth interior surface to 
allow the ready introduction of the wire. 

Must be constructed of or treated with materials which 
will serve as moisture repellants. 




Figure 119 



Must have a substantial outer covering especially de- 
signed to withstand abrasion. 

h. The linings must be secured in position so that they 
cannot be readily removed. 



188 MODERN ELECTRICAL CONSTRUCTION. 

c. The tube must be thoroughly flexible at all temperatures 
at which it is to be used. 

d. Must not crack or break when kinked or flattened out. 

e. Must be sufficiently tough and tenacious to withstand 
severe tension without injury; the interior diameter must not 
be diminished or the tube opened up at any point by the appli- 
cation of a reasonable stretching force. 

/. Must not close to prevent the insertion of the wire 
after the tube has been kinked and straightened out, or 
flattened. 

g. Must not soften injuriously, or cause the wire to stick 
within the tube when subjected to a temperature of 150 degrees 
Fahrenheit. 



51. Switches. 

{For installation rules, see Nos. ly and 22.) 

General Rules. 

a. Must, when used for service switches, indicate, on in- 
spection, whether the current be "on" or "off." 

h. Must, for constant-current systems, close the main cir- 
cuit and disconnect the branch wires when turned "off" ; must 
be so constructed that they shall be automatic in action, not 
stopping between points when started, and must prevent an 
arc between the points under all circumstances. They must 
indicate whether the current be "on" or "off." 

Knife Switches 

{See Figure 120.) 

Knife switches must be made to comply with the following 
specifications, except in those few cases where peculiar design 
allows the switch to fulfill the general requirements in some 
other way, and where it can successfully withstand the test 
of Section i. In such cases, the switch should be submitted 
for special examination before being used. 



FITTINGS^ MATERIALS, ETC. 



189 




c. Base. — Must be mounted on non-combustible, non-ab- 
sorptive, insulating bases, such as slate or por- 
celain. Bases with an area of over twenty-five 
square inches must have at least four sup- 
porting screws. Holes for the supporting 
screws must be so located or countersunk that 
there will be at least one-half inch space, meas- 
ured over the surface, between the head of 
the screw or washer and the nearest live metal 
part, and in all cases when between parts of 
opposite polarity must be countersunk. 

d. Mounting. — Pieces carrying the con- 
tact jaws and hinge clips must be secured to 
the base by at least two screws, or else made 
with a square shoulder or provided with dowel- 
pins, to prevent possible turnings, and the nuts 
Fig. 120 Qj. screw-heads on the under side of the base 

must be countersunk not less than one-eighth 
inch and covered with a waterproof compound which will not 
melt below 150 degrees Fahrenheit. 

e. Hinges. — Hinges of knife switches must not be used 
to carry current unless they are equipped with spring washers, 
held by lock-nuts or pins, so arranged that a firm and secure 
connection will be maintained at all positions of the switch 
blades. 

Spring washers must be of sufficient strength to take up 
any wear in the hinge and maintain a good contact at all 
times. 

f. Metal. — All switches must have ample metal for stiff- 
ness and to prevent rise in temperature of any part of over 
fifty degrees Fahrenheit at full load, the contacts being ar- 
ranged so that a thoroughly good bearing at every point is 
obtained with contact surfaces advised for pure copper blades 
of about one square inch for each seventy-five amperes ; the 
whole device must be mechanically well made throughout. 

g. Cross-Bars. — All cross-bars less than three inches in 
length must be made of insulating material. Bars of three 
inches and over, which are made of metal, to insure greater 
mechanical strength, must be sufficiently separated from the 
jaws of the switch to prevent arcs following from the con- 



190 MODERN ELECTRICAL CONSTRUCTION. 

tacts to the bar on the opening of the switch under any cir- 
cumstances. Metal bars should preferably be covered with 
insulating material. 

To prevent possible turning or twisting the cross-bar must 
be secured to each blade by two screws, or the joints made 
with square shoulders or provided with dowel-pins. 

h. Connections. — Switches for currents of over twenty- 
five amperes must be equipped with lugs, firmly screwed or 
bolted to the switch, and into which the conducting wires shall 
be soldered. For the smaller sized switches simple clamps 
can be employed, provided they are heavy enough to stand 
considerable hard usage. 

Where lugs are not provided, a rugged double V groove 
clamp is advised. A set screw gives a contact at only one 
point is more likely to become loosened, and is almost sure to 
cut into the wire. For the smaller sizes, a screw and waslier 
connection with turned-up lugs on the switch terminal gives a 
satisfactory contact. 

i. Test. — Must operate successfully at 50 per cent over- 
load in amperes and 25 per cent excess voltage, under the most 
severe conditions with which they are liable to meet in practice. 

This test is designed to give a reasonable margin between 
the ordinary rating of the switch and the breaking-down point 
thus securing a switch which can always safely handle its nor- 
mal load. Moreover, there is enough leeway so that a moderate 
amount of overloading would not injure the switch. 

j. Marking. — Must be plainly marked where it will be 
visible, when the switch is installed, with the name of the 
maker and the current and the voltage for which the switch 
is designed. 

k. Spacings. — Spacings must be at least as great as those 
given in the following table. The spacings specified are correct 
for switches to be used on direct-current systems, and can 
therefore be safely followed in devices designed for alternating 
currents. 

125 volts or less: 

Minimum Separation of Minimum 
Nearest Metal Parts of Break- 
Opposite Polarity. Distance, 
For Switchboards and Panel Boards — 

10 amperes or less % inch. i/^ inch. 

11-25 amperes 1 " % 

26-50 " 1^/4 " 1 



FITTINGS, MATERIALS, ETC. 191 

For Individual Switches — 

10 amperes or less 1 inch. % inch. 

11-35 " 1% " 1 

36-100 " . 11/2 " 114 " 

101-300 " 214 " 2 

301-600 " 2% " 21^ " 

601-1000 " 3 " 2% " 

126 to 250 volts: 
For all Switches— 

10 amperes or less li/^ inch. li/4 inch. 



11-35 amperes l^i 

36-100 " 214 

101-300 " 21/2 

301-600 " 2% 

601-1000 " 3 



IV2 
2 

2% 
21/2 
2% 



For 100 ampere switches and larger the above spacings for 

250 volts direct current are also approved for 440 volts alter- 
nating current. Switches with these spacings intended for use 
en alternating-current systems with voltage above 250 volts 
must be stamped with the voltage for which they are designed, 
followed by the letters "A, C." 

251 to 600 volts: 

For all Switches — 

10 amperes or less 3 1/^ inch. 3 inch. 

11-35 amperes 4 " 3^/^ 

36-100 " 41^" 4 

Auxiliary breaks or the equivalent are recommended for 
switches designed for over 300 volts and less than 100 amperes, 
and will be required on switches designed for use in breaking 
currents greater than 100 amperes at a pressure of more than 
300 volts. 

For three-wire Edison systems the separations and break 
distances for plain three-pole knife switches must not be less 
than those required in the above table for switches designed 
for the voltage between the neutral and outside wires. 



Snap Switches. 

(See Figures 121 and 122.) 

Flush, push-button, door, fixture, and other snap switches 
used on constant-potential systems, must be constructed in 
accordance with the following specifications. 

/. Base. — Current-carrying parts must be mounted on non- 
combustible, non-absorptive insulating bases, such as slate or 
porcelain, and the holes for supporting screws should be coun- 
tersunk not less than one-eighth of an inch. There must 



192 



MODERN ELECTRICAL CONSTRUCTION. 



in no case be less than three sixty-fourths of an inch space 
between supporting screws and current-carrying parts. 

Sub-bases of non-combustible, non-absorptive insulating 
material, which will separate the wires at least one-half of 




Figure 121 

an inch from the surface wired over, must be furnished with 
all snap switches used in exposed knob or cleat work. 

m. Mounting. — Pieces carrying contact jaws must be se- 
cured to the base by at least two screws, or else made with 
a square shoulder, or provided with dowel-pins or otherwise 
arranged, to prevent possible turnings ; and the nuts or screw 
heads on the under side of the base must be countersunk not 
less than one-eighth inch, and covered with a waterproof 
compound which will not melt below 150 degrees Fahrenheit. 

11. Metal. — All switches must have ample metal for stiff- 
ness and to prevent rise in temperature of any part of over 




Figure 122 

50 degrees Fahrenheit at full load, the contacts being arranged 
so that a thoroughly good bearing at every point is obtained. 
The whole device must be mechanically well made throughout. 



FITTINGS, MATERIALS, ETC. 193 

In order to meet the above requirements on temperature 
rise without causing excessive friction and wear on current- 
carrying parts, contact surfaces of from 0.1 to 0.15 square inch 
tor each 10 amperes will be required, depending upon the metal 
used and the form of construction adopted. 

o. Insulating Material.— Any material used for insulating 
current-carrj-ing parts must retain its insulating and mechani- 
cal strength when subject to continued use, and must not 
soften at a temperature of 212 degrees Fahrenheit. 

p. Binding Posts. — Binding posts must be substantially 
made, and the screws must be of such size that the threads 
will not strip when set up tight. 

q. Covers. — Covers made of conducting material, except 
face plates for flush switches, must be lined on sides and top 
with insulating, tough and tenacious material at least one- 
thirt5^-second inch in thickness, firmly secured so that it will 
not fall out with ordinary handling. The side lining must ex- 
tend slightly beyond the lower edge of the cover. 

r. Handle or Button. — The handle or button or any ex- 
posed parts must not be in electrical connection with the cir- 
cuit. 

.s". Test. — Must "make" and "break" with a quick snap, 
and must not stop when motion has once been imparted by the 
button or handle. 

Must operate successfully at 50 per cent overload in am- 
peres and 25 per cent excess voltage, under the most severe 
conditions with which they are liable to meet in practice. 

When slowly turned "on and off" at the rate of about two or 
three times per minute, while carrying the rated current, must 
"make and break" the circuit six thousand times before 
failing. 

t. Marking. — Must be plainly marked, where it may be 
readily seen after the device is installed, with the name or 
trade mark of the maker and the current and voltage for 
which the switch is designed. 

On flush switches these markings may be placed on the 
back of the face plate or on the sub-plate. On other types 
they must be placed on the front of the cap, cover, or plate. 

Switches which indicate whether the current is "on" or 
"off" are recommended. 



194 



MODERN ELECTRICAL CONSTRUCTION. 



52. Cut-Outs and Circuit-Breakers. 

(Sec Figure 123.) 

{For installation rules, see Nos. ly and 21.) 

General Rules. 

- a. Must be supported on bases of non-combustible, non- 
absorptive insulating material. 

b. Cut-outs must be of plug or cartridge type, when not 
arranged in approved cabinets, so as to obviate any danger of 
the melted fuse metal coming in contact with any substance 
which might be ignited thereby. 

c. Cut-outs must operate successfully on short-circuits, 
under the most severe conditions with which they are liable to 




Single Pole. 



Figure 123 



Double Pole. 



meet in practice, at 25 per cent above their rate of voltage and 
the fuses rated at 50 per cent above the current for which the 
cut-out is designed. 

There is always the possibility of a larger fuse being put 
in the cut-out than it was designed for. Again, the voltage in 
most plants can, under some conditions, rise considerably 
above the normal. The need of some margin, as a factor of 
safety to prevent the cut-outs from being ruined in ordinary 
service, is therefore evident. 

The most severe service which can be required of a cut-out 
in practice is to open a "dead short-circuit" with only one 
fuse blowing, and it is with these conditions that all tests 
should be made. (See Section j.) 



FITTINGS, MATERIALS, ETC. 



195 



d. Circuit-breakers must operate successfully on short-cir- 
cuits, under the most severe conditions with which they are 
hable to meet in practice, when set at 50 per cent above the 
current, and with a voltage 25 per cent above that for which 
they are designed. 

For the same reason as in Section c. 

e. Must be plainly marked where it will always be visible, 
with the name of the maker, and current and voltage for which 
the device is designed. 



Link-Fuse Cut-Outs. 

{See Figure 124.) 

The following rules are intended to cover open link fuses 
mounted on slate or marble bases, including- switchboards, 
tablet-boards, and single fuse-blocks. They do not apply to 
fuses mounted on porcelain bases, to the ordinary porcelain 
cut-out blocks, enclosed fuses, or any special or covered type 
of fuse. When tablet-boards or single fuse-blocks with such 
open link fuses on them are used in general wiring, they must 
be enclosed in cabinet boxes made to meet the requirements of 
No. 54. This is necessary, because a severe flash may occur 
when such fuses melt, so that they would be dangerous if 
exposed in the neighborhood of any combustible material. 

f. Base. — Must be mounted on slate or marble bases. 
Bases with an area of over twenty-live square inches must 





Figure 124 



Figure 125 



have at least four supporting screws. Holes for supporting 
screws must be kept outside of the area included by the out- 
side edges of the fuse-block terminals, and must be so located 
or countersunk that there will be at least one-half an inch 



196 MODERN ELECTRICAL CONSTRUCTION. 

space, measured over the surface, between the head of the 
screw or washer and the nearest live part. 

g. Mounting. — Nuts or screw-heads on the under side 
of the base must be countersunk not less than one-eighth inch, 
and covered with a waterproof compound which will not melt 
below 150 degrees Fahrenheit. 

h. Metal. — All fuse-block terminals must have ample metal 
for stiffness and to prevent rise in temperature of any part of 
over 50 degrees Fahrenheit at full load. Terminals, as far as 
practicable, should be made of compact form instead of being 
rolled out in thin strips; and sharp edges or thin projecting 
pieces as on winged thumb nuts and the like should be avoided. 
Thin metal, sharp edges and projecting pieces are much more 
likely to cause an arc to start than a more solid mass of metal. 
It is a good plan to round all corners of the terminals and to 
chamfer the edges. 

i. Connections. — Clamps for connecting the wires to the 
fuse-block terminals must be of solid, rugged construction, so 
as to insure a thoroughly good connection and to withstand 
considerable hard usage. For fuses rated at over fifty am- 
peres, lugs firmly screwed or bolted to the terminals and into 
which the conducting wires are soldered must be used. 

See not3 under No. 51 h. 

;. Test. — Must operate successfully when blowing only 
one fuse at a time on short-circuits with fuses rated at 50 
per cent above and with a voltage 25 per cent above the 
current and voltage for which the cut-out is designed. 

k. Marking.— Must be plainly marked, where it will be 
visible when the cut-out block is installed, with the name of 
the maker and the current and the voltage for which the 
block is designed. 

/. Spacings.— Spacings must be at least as great as those 
given in the following table, which applies only to plain, open 
link-fuses mounted on slate or marble bases. The spacings 
given are correct for fuse-blocks to be used on direct-cur- 
rent systems, and can therefore be safely followed in devices 
designed for alternating currents. If the copper fuse-tips over- 



FITTINGS, MATERIALS, ETC. 197 

hang the edges of the fuse-block terminals, the spacings should 
be measured between the nearest edges of the tips. 

125 volts or less: 

Minimum Separation of Minimum 
Nearest Metal Parts of Break- 
Opposite Polarity. Distance. 

10 amperes or less % inch. % inch. 

11-100 amperes 1 " % " 

101-300 " 1 " 1 

301-1000 " 114 " IV4. " 

126 to 250 volts: 

10 amperes or less li/^ inch. 1^^ inch. 

11-100 amperes 1% " 1% " 

101-300 " 2 " 11/2 " 

301-1000 " 21/2 " 2 

A space must be maintained between fuse terminals of the 
same polarity of at least one-half inch for voltages up to 125 
and of at least three-quarter inch for voltages from 126 to 250. 
This is the minimum distance allowable, and greater separation 
should be provided when practicable. 

For 250 volt boards or blocks with the ordinary front-con- 
nected terminals, except where these have a mass of compact 
form, equivalent to the back-connected terminals usually found 
in switchboard work, a substantial barrier of insulating mate- 
rial, hot less than one-eighth of an inch in thickness, must be 
placed in the "break gap — this barrier to extend out from the 
base at least one-eighth of an inch farther than any bare live 
part of the fuse-block terminal, including binding screws, nuts 
and the like. (Figure 125.) 

For three-wire systems cut-outs must have the break-dis- 
tance required for circuits of the potential of the outside wires. 

Enclosed-Fuse Cut-Outs, — Plug and Cartridge Type. 

{See Figure 126.) 

m. Base. — Must be made of non-combustible, non-ab- 
sorptive insulating material. Blocks with an area of over 
twenty-five square inches must have at least four supporting 
screws. Holes for supporting screws must be so located or 
countersunk that there will be at least one-half of an inch 
space, measured over the surface, between the screw-head or 
washer and the nearest live metal part, and in all cases when 
between parts of opposite polarity must be countersunk. 

n. Mounting. — Nuts or screw-heads on the under side of 
the base must be countersunk at least one-eighth of an inch 



198 MODERN ELECTRICAL CONSTRUCTION. 

and covered with a waterproof compound which will not melt 
below 150 degrees Fahrenheit. 

o. Terminals. — Terminals of such a design that the block 
cannot be easily fused with anything but approved enclosed 
fuses are recommended for blocks of all capacities, and will 
be required on blocks having a rated capacity of sixty am.- 





Figure 126 

peres or less. They must be secured to the base by two 
screws or the equivalent, so as to prevent them from turning, 
and must be so made as to secure a thoroughly good contact 
with the fuse. 

p. Connections. — Clamps for connecting wires to the ter- 
minals must be of a design which will ensure a thoroughly 
good connection, and must be sufficiently strong and heavy to 
withstand considerable hard usage. For fuses rated to carry 
over sixty amperes, lugs firmly screwed or bolted to the ter- 
minals and into which the connecting wires shall be soldered 
must be used. 

q. Classification. — Must be classified as regards both cur- 
rent and voltage, and must be so designed that the bases of 
one class cannot be used with fuses of another class rated for 
a higher current or voltage. The following classification is 
recommended : — 

0-250 Volts. 251-600Volts. 

0- 30 amperes. 0- 30 amperes. 

31- 60 " 31- 60 

61-100 " 61-100 

101-200 " 101-200 

201-300 " 201-300 

301-500 " 301-500 

r. Design. — Must be of such a design that it wil not be 
easy to form accidental short-circuits across live metal parts 
of opposite polarity on the block or on the fuses in the block. 

s. Marking. — Must be marked, where it will be plainly 



FITTINGS/ MATERIALS, ETC. 199 

visible when the block is installed, with the name of the maker 
and the voltage and range of current for which it is designed. 

53. Fuses. 

{For installation rules, sec Nos. I'j and 21.) 

Link Fuses. 

a. Terminals, — Must have contact surfaces or tips of 
harder metal, having perfect electrical connections with the 
fusible part of the strip. 

The use of the hard metal tip is to afford a strong mechan- 
ical bearing for the screws, clamps, or other devices provided 
for holding the fuse. 

h. Rating. — Must be stamped with about 80 per cent of 
the maximum current which they can carry indefinitely, thus 
allowing about 25 per cent overload before the fuse melts. 

With naked open fuses, of ordinary shapes and with not 
over 500 amperes capacity, the minimum current which Will 
melt them in about five minutes may be safely taken as the 
melting point, as the fuse practically reaches its maximum 
temperature in this time. Witli larger fuses a longer time is 
necessary. This data is given to facilitate testing. 

c. Marking. — Fuse terminals must be stamped with the 
maker's name or initials, or with some known trade mark. 



Enclosed Fuses, — Plug and Cartridge Type. 

{See Figure 126.) 

d. Construction. — The fuse plug or cartridge must be 
sufficiently dust-tight so that lint and dust cannot collect 
around the fusible wire and become ignited when the fuse is 
blown. 

The fusible wire must be attached to the plug or cartridge 
terminals in such a way as to secure a thoroughly good con- 
nection and to make it difficult for it to be replaced when 
melted. 

e. Classification. — Must be classified to correspond with 
the different classes of cut-out blocks, and must be so designed 



200 



MODERN ELECTRICAL CONSTRUCTION. 



that it will be impossible to put any fuse of a given class into 
a cut-out block which is designed for a current or voltage 
lower than that of the class to which the fuse belongs. 

f. Terminals. — The fuse terminals must be sufficiently 
heavy to ensure mechanical strength and rigidity. 

g. Rating. — Must be rated at 80 per cent of the maximum 
current which they will carry indefinitely, and must open the 
circuit within five minutes when a current 50 per cent greater 
than their rated capacity is passed through them. 

h. Marking. — Must be marked, where it will be plainly 




Three-Wire Mains 
Figure 127 

visible, with the name or trade mark of the maker and the 
voltage and current for which the fuse is designed. 

i. Temperature Rise. — The temperature of the exterior 
of the fuse enclosure, must not rise more than 125 degrees 



FITTINGS, MATERIALS, ETC. 201 

Fahrenheit above that of the snrrroimdmg air when the fuse 
is carrying the current for which it is rated. 

y. Test. — Must not hold an arc or throw out melted metal 
or sufficient flame to ignite easily inflammable material on or 
near the cut-out, when only one fuse is blown at a time on a 
short-circuit, on a system having a capacity of 300 K. W. 
or over, at the voltage for which the fuse is rated. 

A number of fuses having considerable merit will probably 
not fully stand this test. Such fuses will be carefully ex- 
amined and tested, and approved with such limitations as 
safety requires. For example, a fuse which mig-ht be quite 
satisfactory in the small sizes or with a moderate amount of 
resistance in circuit, but which under more severe conditions 
would arc considerably, might be approved without reservation 
up to certain limits and approved beyond these limits only 
when enclosed in cabinets or safely removed from combustible 
materials. Greater definiteness appears impossible in the 
present state of the art. 

53 A. Tablet and Panel Boards. 

(vS'^^ Figure 127.) 

The following minimum distance between bare live metal 
parts (bus-bars, etc.) must be maintained: — 

Between parts of opposite polarty Between parts of 

except at switches and link fuses. same polarity. 

When mounted on When held free At link 

the same surface. in the air. fuses. 

0-125 volts % inch. % inch. % inch. 

126-250 volts 11^ " % " % " 

At switches or enclosed fuses, parts of the same polarity 
may be placed as close together as convenience in handling 
will allow. 

It should be noted that the above distances are the mini- 
mum allowable, and it is urged that greater distances be 
adopted wherever the conditions will permit. 

The spacings given in the first column apply to the branch 
conductors where enclosed fuses are used. Where link fuses 
or knife switches are used, the spacings must be at least as 
great as those required \)y Nos. 51 and 52. 

The spacings given in the second column apply to the dis- 
tance between the raised main bars, and between these bars and 
the branch bars over v,^hich they pass. 

The spacings given in the third column are intended to 
prevent the melting of a link fuse by the blowing of an ad- 
jacent fuse of the same polarity. 



202 



MODERN ELECTRICAL CONSTRUCTION. 




54. Cut-Out Cabinets. 

a. Material. — Cabinets must be siib- 

<^^antially constructed of non-combusti- 

1 le, non-absorptive material, or of wood. 

When wood is use dth« inside of the cabi- 
t must be completely lined with a non- 
mbustible insulating material. Slate or 
arble at least one-quarter inch in thick- 
ss is strongly recommended for such 

1 ling, but, except with metal conduit 
stems, asbestos board at least one- 
j-hth inch in thickness may be used in 

1 y places if firmly secured by shellac 
id tacks. 

With metal conduit systems the lining 
either the box or the gutter must be 
e-sixteenth inch galvanized, painted 

or enameled iron, or preferably one- 
Fig. 128. quarter inch slate or marble. (Figure 

128.) 

The object of the lining of such cut-out cabinets or gutters 
is to render the same approximately fireproof in case of short 
circuit after the wires leave the protecting metal conduits. 

With wood cabinets the wood should be thoroughly filled 
and painted before the lining is put in place. 

h. Door. — The door must close against a rabbet, so as to 
be perfectly dust-tight. Strong hinges and a strong hook or 
catch are required. Glass doors must be glazed with heavy 
plate glass, not less than three-sixteenths of an inch in thick- 
ness, and panes should not exceed one foot in width. A space 
of at least two inches must be allowed between the fuses and 
the door. This is necessary to prevent cracking or breaking 
by the severe blow and intense heat which may be produced 
under some conditions. 

A cabinet is of little use unless the door is kept tightly- 
closed, and especial attention is therefore called to the impor- 
tance of having a strong and reliable catch or other fastening. 
A spring catch is advised if a good one can be obtained, but 
most of tliose sold for use on cupboards, etc., are so small 
that they fail to catch when the door shrinks a little, or are 
so weak that they soon give out. 

c. Bushings. — Bushings through which wires enter must 
fit tightly the holes in the box, and must be of approved con- 



FITTINGS, MATERIALS, ETC. 



203 



struction. The wires should completely fill the holes in the 
bushings, using tape to build up the wire, if necessary, so as 
to keep out the dust. 

Rule 54 A. New Rule — Rosettes. 

{See Figure I2g.) 

Ceiling- rosettes, both fused and fuseless, must be con- 
structed in accordance with tlie following specifications: 

a. Base. — Current-carrying parts must be mounted on non- 
combustible, non-absorptive insulating bases. There should be 
no openings through the rosette base except those for the 





Figure 129 



supporting screws and in the concealed type for the con- 
ductors also, and these openings should not be made any 
larger than necessary. 

There must be at least one-quarter inch space, measured 
over the surface, between supporting screws and current- 
carrying parts. The supporting screws must be so located 
or countersunk that the flexible cord cannot come in con- 
tact with them. 

Bases for the knob and cleat type must have at least two 
holes for supporting screws ; must be high enough to keep the 
wires and terminals at least one-half inch from the surface 
to which the rosette is attached, and must have a porcelain 
lug under each terminal to prevent the rosette from being 
placed over projections which would reduce the separation to 
less than one-half inch. 

Bases for the moulding and conduit box types must be 
high enough to keep the wires and terminals at least three- 
eighths inch from the surface wired over. 



204 MODERN ELECTRICAL CONSTRUCTION. 

b. Mounting. — Contact pieces and terminals must be se- 
cured in position by at least two screws, or made with a square 
shoulder, or otherwise arranged to prevent turning. 

The nuts or screw heads on the under side of the base must 
be countersunk not less than one-eighth inch and covered with 
a waterproof compound which will not melt below 150 degrees 
Fahrenheit. 

c. Terminals. — Line terminal plates must be at least 
,07 of an inch in thickness, and terminal screws must not 
be smaller than No. 6 standard screw with about 32 threads 
per inch. 

Terminal plates for the flexible cord and for fuses must 
be at least .06 of an inch in thickness, and the terminal screws 
must not be smaller than No. 5 standard screw with about 40 
threads per inch. 

d. Cord Inlet. — The diameter of the cord inlet hole should 
measure 13/32" in order that standard portable cord may be 
used. 

e. Knot Space. — Ample space must be provided for a 
substantial knot tied in the cord as a whole. 

All parts of the rosette upon which the knot is likely to 
bear must be smooth and well rounded. 

/. Cover. — When the rosette is made in two parts, the 
cover must be secured to the base so that it 'will not work 
loose. 

In fused rosettes, the cover must fit closely over the base 
so as to prevent the accumulation of dust or dirt on the inside, 
and also to prevent any flash or melted metal from being 
thrown out when the fuses melt. 

g. Markings. — Must be plainly marked where it may read- 
ily be seen after the rosette has been installed, with the name or 
trade mark of the manufacturer, and the rating in amperes 
and volts. Fuseless rosettes may be rated 3 amperes, 250 volts ; 
fused rosettes, with link fuses, not over 2 amperes, 125 volts. 

g. Test. — Fused rosettes must have a fuse in each pole 
and must operate successfully when short-circuited on the vol- 
tage for which they are designed, the test being made with 
the two fuses in circuit. 

NOTE. — When link fuses are used the test shall be made with 
fuse wire which melts at about 7 amperes in one inch lengths. 
The larger fuse is specified for the test in order to more nearly 



FITTINGS, MATERIALS, ETC. 205 

approximate the severe conditions obtained when only one 
2-ampere fuse (the rating- of the rosette) is blown at a time. 

Fused rosettes equipped with enclosed fuses are much 
preferable to the link fuse rosettes. 

55. Sockets. 

{See Figure 130.) 

{For installation rules, see No. 27.) 

Sockets of all kinds, including- wall receptacles, must be 
constructed in accordance with the following specifications: 

a. Standard Sizes. — The standard lamp socket must be 
suitable for use on any voltage not exceeding 250 and with 
any size lamp up to fifty candle-power. For lamps larger than 
fifty candle-power a standard keyless socket may be used, or 
if a key is required, a special socket designed for the current 
to be used must be made. Any special sockets must follow the 
general spirit of these specifications. 

h. Marking. — The standard socket must be plainly marked 
250v., 50 c. p., and with the manufacturer's name or regis- 
tered trade mark. Special sockets must be marked with the 
current and voltage for which they are designed. 

c. Shell. — Metal used for shells must be moderately hard, 
but not hard enough to be brittle or so soft as to be easily 




Figure 130 

dented or knocked out of shape. Brass shells must be at least 
thirteen one-thousandths of an inch in thickness, and shells 
of any other material must be thick enough to give the same 
stiffness and strength as the required thickness of brass. 

d. Lining. — The inside of the shells must be lined with 
insulating material, which must absolutely prevent the shell 
from becoming a part of the circuit, even though the wires 
inside the socket should start from their position under the 
binding screws. 



206 MODERN ELECTRICAL CONSTRUCTION. 

The material used for lining must be at least one thirty- 
second of an inch in thickness, and mast be tough and tena- 
cious. It must not be injuriously affected by the heat from the 
largest lamp permitted in the socket, and must leave water 
in which it is boiled practically neutral. It must be so firmly 
secured to the shell that it will not fall out with ordinary 
handling of the socket. It is preferable to have the lining in 
one piece. 

The cap must also be lined, and this lining must comply 
with the requirements for shell linings. 

The shell lining should extend beyond the shell far enough 
so that no part of the lamp base is exposed when a lamp is in 
the socket. 

e. Cap. — Caps, when of sheet brass, must be at least thir- 
teen one-thousandths of an inch in thickness, and when cast 
or made of other metals must be of equivalent strength. The 
inlet piece, except for special sockets, must be tapped with 
a standard one-eighth-inch pipe thread. It must contain 
sufficient metal for a full, strong thread, and when not in one 
piece with the cap, must be joined to it in such a way as to 
give the strength of a single piece. 

There must be sufficient room in the cap to enable the 
ordinary wireman to easily and quickly make a knot in the 
cord and to push it into place in the cap without crowding. 
All parts of the cap upon which the knot is likely to bear must 
be smooth and well insulated. 

The cap lining called for in the note to Section d will pro- 
vide a sufficiently smooth and well-insulated surface for the 
knot to bear upon. 

Sockets with an outlet threaded for three-eighths inch 
pipe will, of course, be approved where circumstances demand 
their use. This size outlet is necessary with most stiff 
pendants and for the proper use of reinforced flexible cord, as 
explained in the note to No. 28 cZ. 

f. Frame and Screws. — The frame which holds the mov- 
ing parts must be sufficiently heavy to give ample strength and 
stiffness. 

Brass pieces containing screw threads must be at least 
six one-hundredths of an inch in thickness. 

Binding post screws must not be smaller than No. 5 stand- 
ard screw with about 40 threads per inch. 

g. Spacing. — Points of opposite polarity must every- 



FITTINGS, MATERIALS, ETC. 207 

where be kept not less than three sixty-fourths of an inch 
apart, unless separated by a reliable insulation. 

• h. Connections. — The connecting points for the flexible 
cord must be made to very securely grip a No. 16 or 18 B. 
& S. gage conductor. A turned-up lug, arranged so that the 
cord may be gripped between the screw and the lug in such 
a way that it cannot possibly come out, is strongly advised. 

/. Lamp Holder. — The socket must firmly hold the lamp 
in place so that it cannot be easily jarred out, and must pro- 
vide a contact good enough to prevent undue heating with the 
maximum current allowed. The holding pieces, springs, and 
the like, if a part of the circuit, must not be sufficiently ex- 
posed to allow them to be brought in contact with anything 
outside of the lamp and socket. 

y. Base. — With the exception of the lining all parts of 
insulating material inside the shell must be made of por- 
celain. 

k. Key. — The socket key-handle must be of such a ma- 
terial that it will not soften from the heat of a fifty candle- 
power lamp hanging downwards from the socket in air at 70 
degrees Fahrenheit, and must be securely, but not necessarily 
rigidly, attached to the metal spindle which it is designed to 
turn. 

/. Sealing. — All screws In porcelain pieces, which can be 
firmly sealed in place, must be so sealed by a waterproof com- 
pound which will not melt below 200 degrees Fahrenheit. 

m. Putting Together. — The socket as a whole must be so 
put together that it will not rattle to pieces. Bayonet joints or 
an equivalent are recommended. 

n. Test. — The socket, when slowly turned "on and off" 
at the rate of about two or three times per minute, while 
carrying a load of one ampere at 250 volts, must "make and 
break" the circuit 6,000 times before failing. 

o. Keyless Sockets. — Keyless sockets of all kinds must 
comply with the requirements for key sockets as far as they 
apply. 

p. Sockets of Insulating Material. — Sockets made of 
porcelain or other insulating material must conform to the 



208 MODERN ELECTRICAL CONSTRUCTION. 

above requirements as far as they apply, and all parts must 
be strong enough to withstand a moderate amount of hard 
usage without breaking. 

Porcelain shell sockets being subject to breakage, and 
constituting a hazard when broken, will not be accepted for 
use in places where they would be exposed to hard usage. 

q. Inlet Bushing. — When the socket is not attached 

to a fixture, the threaded inlet must be provided with a strong 
insulating bushing having a smooth hole at least nine thirty- 
seconds of an inch in diameter. The edges of the bushing 
must be rounded and all inside fins removed, so that in no place 
will the cord be subjected to the cutting or wearing action of 
a sharp edge. 

Bushings for sockets having an outlet threaded for three- 
eights-inch pipe should have a hole thirteen thirty-seconds of 
an inch in diameter, so that they will accommodate approved 
reinforced flexible cord. 



56. Hanger-Boards. 

{See Figure 131.) 

a. Hanger-boards must be so constructed that all wires 
and current-carrying devices thereon will be exposed to view 
and thoroughly insulated by being mounted on a non-com- 





Figure 131 

bustible, non-absorptive insulating substance. All switches 
attached to the same must be so constructed that they shall 
be automatic in their action, cutting off both poles to the lamp, 
not stopping between points when started and preventing an 
arc between points under all circumstances. 



FITTINGS, MATERIALS, ETC. 



209 



57. Arc Lamps. 

(See Figure 132.) 

(For installation rules, see Nos. 19 and 29.) 

a. Must be provided with reliable stops to prevent car- 
bons from falling out in case the clamps become loose. 

b. All exposed parts must be carefully insulated from the 
circuit. 

c. Must, for constant-current systems, be provided with 
an approved hand switch, and an automatic switch that will 

shunt the current around the carbons, 
should they fail to feed properly. 

The hand switch to be approved, if 
placed anywhere except on the lamp 
itself, must comply with requirements 
for switches on hangerboards as laid 
down in No. 56. 

58. Spark Arresters. 

(See Figure 132.) 

{For installation rules, see Nos. 19 c 

and 2Q c.) 

a. Spark arresters must so close 
the upper orifice of the globe that it 
will be impossible for any sparks, 
thrown out by the carbons, to escape. 




Fig. 132. 



59. Insulating Joints. 

(See No. 26 a.) 

a. Must be entirely made of material that will resist the 
action of illuminating gases, and will not give way or soften 
under the heat of an ordinary gas flame or leak under a mod- 
erate pressure. Must be so arranged that a deposit of moisture 
will not destroy the insulating effect; must show a dielectric 
strength between gas-pipe attachments sufficient to resist 
throughout five minutes the application of an electro-motive 
force of 4,000 volts ; and must be sufficiently strong to resist 
the strain to which they are liable to be subjected during instal- 
lation. 



210 MODERN ELECTRICAL CONSTRUCTION. 

b. Insulating joints having soft rubber in their construc- 
tion will not be approved. 

60. Rheostats. 

(For installation rules, see Nos. 4 a and 8 c.) 

a. Materials. — Must be made entirely of non-combustible 
materials except such minor parts as handles, magnet insula- 
tion, etc. 

All segments, lever arms, etc., must be mounted on non- 
combustible, non-absorptive, insulating material. 

Resistance boxes are used for the express purpose of op- 
posing the passage of current, and are therefore very liable to 
get exceedingly hot. Hence they should have no combustible 
material in their construction. 

b. Construction. — Must have legs which will keep the 
current-carrying parts at least one inch from the surface on 
which the rheostat is mounted. 

The construction throughout must be heavy, rugged, and 
thoroughly workmanlike. 

c. Connections. — Clamps for connecting wires to the 
terminals must be of a design which will ensure a thoroughly 
good connection, and must be sufficiently strong and heavy to 
withstand considerable hard usage. For currents above fifty 
amperes, lugs firmly screwed or bolted to the terminals, and 
into which the connecting wires shall be soldered, must be 
used. 

Clamps or lugs will not be required when leads designed 
for soldered connections are provided. 

d. Marking. — Must be plainly marked, where it may be 
readily seen after the device is installed, with the rating and 
the name of the maker; and the terminals of motor-starting 
rheostats must be marked to indicate to what part of the circuit 
each is to be connected, as "line," "armature," and "field." 

e. Contacts. — The design of the fixed and movable con- 
tacts and the resistance in each section must be such as to 
secure the least tendency toward arcing and roughening of the 
contacts, even with careless handling or the presence of dirt. 

In motor-starting rheostats, the contact at which the cir- 
cuit is broken by the lever arm when moving from the running 



FITTINGS, MATERIALS, ETC. 211 

to the starting position, must be so designed that there will 
be no detrimental arcing. The final contact, if any, on which 
the arm is bronght to rest in the starting position must have 
no electrical connection. 

Experience has shown that sharp edges and segments of 
thin material help to maintain an arc, and it is recommended 
that these be avoided. Segments of heavy construction have 
a considerable cooling effect on the arc, and rounded corners 
tend to spread it out and thus dissipate it. 

/. No-voltage release. — Motor-starting rheostats must 
be so designed that the contact arm cannot be left on interme- 
diate segments, and must be provided with an automatic device 
which will interrupt the supply circuit before the speed of the 
motor falls to less than one-third of its normal value. 

g. Overload-release. — Overload-release devices which are 
inoperative during the process of starting a motor will not be 
approved, unless other circuit-breakers or fuses are installed 
in connection with them. 

If, for instance, the overload-release device simply releases 
the starting arm and allows it to fly back and break the circuit, 
it is inoperative while the arm is being moved from the start- 
ing to the rvmning position. 

h. Test. — Must, after 100 operations under the most 
severe normal conditions for which the device is designed, 
show no serious burning of the contacts or other faults, and 
the release mechanism of motor-starting rheostats must not be 
impaired by such a test. 

Field rheostats, or main-line regulators intended for con- 
tinuous use, must not be burned out or depreciated by carrying 
the full normal current on any step for an indefinite period. 
Regulators intended for intermittent use (such as on electric 
cranes, elevators, etc.) must be able to carry their rated cur- 
rent on any step for as long a time as the character of the 
apparatus which they control will permit them to be used 
continuously. 

61. Reactive Coils and Condensers. 

a. Reactive coils must be made of non-combustible 
material, mounted on non-combustible bases and treated, in 
general, as sources of heat. 

b. Condensers must be treated like other apparatus oper- 
ating with equivalent voltage and currents. They must have 



212 MODERN ELECTRICAL CONSTRUCTION. 

non-combustible cases and supports, and must be isolated from 
all combustible materials and, in general, treated as sources 
of heat. 

62. Transformers. 

{For installation rules, see Nos. ii, 13, 13 A and 36.) 

a. Must not be placed in any but metallic or other non- 
combustible cases. 

On account of the possible dangers from burn-outs in the 
coils. (See note undei' No. 11 a.) 

It is advised that every transformer be so designed and 
connected that the middle point of the secondary coil can 
be reached if, at any future time, it should be desired to 
ground it. 

b. Must be constructed to comply with the following tests : 

1. Shall be run for eight consecutive hours at full -load 

in watts under conditions of service, and at the 
end of that time the rise in temperature, as meas- 
ured by the increase of resistance of the primary 
coil, shall not exceed 135 degrees Fahrenheit. 

2. The insulation of transformers when heated shall 

withstand continuously for five minutes a differ- 
ence of potential of 10,000 volts (alternating) be- 
tween the primary and secondary coils and be- 
tween the primary coils and core, and a no-load 
"run" at double voltage for thirty minutes. 

63. Lightning Arresters. 

(For installation rules, see No. 5.) 

a. Must be mounted on non-combustible bases ; must be so 
constructed as not to maintain an arc after the discharge has 
passed ; must have no moving parts. 



Glass E. 

MISCELLANEOUS. 

64. Signaling Systems. 

Governing wiring for telephone, telegraph, district mes- 
senger and call-bell circuits, fire and burglar alarms, and 
all similar systems. 

a. Outside wires should be run in underground ducts or 
strung on poles, and, as far as possible, kept off of buildings, 
and must not be placed on the same cross-arm with electric 
light or power wires. They should not occupy the same duct, 
manhole or handhole of conduit systems with electric light or 
power wires. 

Single manholes, or handholes, may be separated into sec- 
tions by means of partitions of brick or tile so as to be con- 
sidered as conforming with the above rule. 

h. When outside wires are run on same pole with electric 
light or power wires, the distance between the two inside pins 
of each cross-arm must not be less than twenty-six inches. 

c. All aerial conductors and underground conductors 
which are directly connected to aerial wires must be provided 
with some approved protective device, which must be located 
as near as possible to the point where they enter the building, 
and not less than six inches from curtains or other inflammable 
material. 

d. If the protector Is placed Inside of building, wires from 
outside support to binding-posts of protector, must comply 
with the following requirements : 

1. Must be of copper, and not smaller than No. 18 B. & 

S. gage. 

2. Must have an approved rubber insulating covering 

(see No. 41). 

3. Must have drip loops in each wire Immediately out- 

side the building. 

4. Must enter buildings through separate holes sloping 

upward from the outside; when practicable, holes 
to be bushed with non-absorptive, non-combustible 
insulating tubes extending through their entire 
length. Where tubing is not practicable the wires 
shall be wrapped with two layers of insulating 
tape. 



214 MODERN ELECTRICAL CONSTRUCTION. 

5. Must be supported on porcelain insulators, so that 

they will not come in contact with anything other 
than their designed supports. 

6. A separation between wires of at least two and one- 

half inches must be maintained. 

In case of crosses these wires may become a part of a 
high-voltage circuit, so that care similar to that given high- 
voltage circuits is needed in placing them. Porcelain bushings 
at the entrance holes are desirable, and this requirement is 
rnly waived under adverse conditions, because the state of 
t e art in this type of wiring makes an absolute requirement 
inadvisable. 

e. The ground wire of the protective device shall be run in 
accordance with the following requirements : 

1. Shall be of copper, and not smaller than No. 18 B. & 

S. gage. 

2. Must have an approved rubber insulating covering 

(see No. 41). 

3. Must run in as straight a line as possible to a good, 

permanent ground, to be made by connecting to 
water or gas pipe, preferably water pipe. If gas 
pipe is used, the connection, in all cases, must be 
made between the meter and service pipes. In 
the absence of other good ground, connection must 
made to a metallic plate or bunch of wires buried 
in permanently moist earth. 

In attaching a ground wire to a pipe it is often difficult 
to make a thoroughly reliable solder joint. It is better, there- 
fore, where possible, to carefully solder the wire to a brass 
plug, which may then be firmly screwed into a pipe fitting. 

Where such joints are made under ground they should be 
thoroughly painted and taped to prevent corrosion. 

f. The protector to be approved must comply with the fol- 
lowing requirements : 

1. Must be mounted on non-combustible, non-absorptive 

insulating bases, so designed that when the pro- 
tector is in place, all parts which may be alive will 
be thoroughly insulated from the wall to which 
the protector is attached. 

2. Must have the following parts : 

A lightning arrester which will operate with a differ- 
ence of potential between wires of not over 500 
volts, and so arranged that the chance of acci- 
dental grounding is reduced to a minimum. 



MISCELLANEOUS. 215 

A fuse designed to open the circuit in case the wires 
become crossed with Hght or power circuits. The 
fuse must be able to open the circuit without arc- 
ing or serious flashing when crossed with any 
ordinary commercial light or power circuit. 
A heat coil, if the sensitiveness of the instrument de- 
mands it, which will operate before a sneak cur- 
rent can damage the instrument the protector is 
guarding. 
Heat coils are necessary in all circuits normally closed 
through magnet windings, which cannot indefinitely carry a 
current of at least five amperes. 

The heat coil is designed to warm up and melt out with 
a current large enough to endanger the instruments if con- 
tinued for a long time, but so small that it would not blow 
the fuses ordinarily found necessary for such instruments. 
These smaller currents are often called "sneak" currents. 

3. The fuses must be so placed as to protect the arrester 

and heat coils, and the protector terminals must 

be plainly marked "line/* "instruments," "ground." 

g. Wires beyond the protector, except where bunched, 

must be neatly arranged and securely fastened in place in some 

convenient, workmanlike manner. They must not come nearer 

than six inches to any electric light or power wire in the 

building unless encased in approved tubing so secured as to 

prevent its slipping out of place. 

The wires would ordinarily be insulated, but the kind of 
insulation is not specified, as the protector is relied upon to 
stop all dangerous currents. Porcelain tubing or approved 
flexible tubing may be used for encasing wires where re- 
quired as above. 

h. Wires connected with outside circuits, where bunched 
together within any building, or inside wires, where laid in 
conduits or ducts with electric light or power wires, must have 
fire-resisting coverings, or else must be enclosed in an air- 
tight tube or duct. 

It is feared that if a burnable insulation were used, a 
chance spark might ignite it and cause a serious fire, for 
many insulations contain a large amount of very readily 
burnable matter. 

55. Electric Gas Lighting. 

a. Electric gas lighting must not be used or the same fix- 
ture with the electric light. 



216 MODERN ELECTRICAL CONSTRUCTION. 

65A. Moving Picture Machines. 

a. Top reel must be encased in an iron box with hole at 
the bottom only large enough for film to pass through, and 
cover so arranged that this hole can be instantly closed. No 
solder to be used in the construction of this box. 

b. A box must be used for receiving the film after being 
shown, made of galvanized iron with a hole in the top only 
large enough for the film to pass through freely, with a cover 
so arranged that this hole can be instantly closed. An opening 
may be placed at the side of the box to take the film out, with 
a door hung at the top, so arranged that it cannot be entirely 
opened, and provided with a spring catch to lock it closed. 
No solder to be used in the construction of this box. 

c. The handle or crank used in operating the machine must 
be secured to the spindle or shaft so that there will be no lia- 
bility of its coming off and allowing the film to stop in front 
of the lamp. 

d. A shutter must be placed in front of the condenser, 
arranged so as to be normally closed, and held open by pres- 
sure of the foot. 

e. A metal pan must be placed under the arc lamp to catch 
all sparks. 

/. Extra films must be kept in metal box with tight-fitting 
covers. 

66. Insulation Resistance. 

The wiring in any building must test free from grounds ; 
I. e., the complete installation must have an insulation between 
conductors and between all conductors and the ground (not 
including attachments, sockets, receptacles, etc.) not less than 
that given in the following table : 

Up to 5 amperes 4,000,000 ohms . 

10 " 2,000,000 

25 " 800,000 

50 " 400,000 

100 " 200,000 

200 " 100,000 

400 " 50,000 

800 " 25,000 

1,600 " 12,500 

The test must be made with all cut-outs and safety de- 
vices in place. If the lamp sockets, receptacles, electroliers, 
etc.), are also connected, only one-half of the resistance speci- 
fied in the table will be required. 



PRACTICAL HINTS. 21? 

PRACTICAL HINTS. 

A full description of the Wheatstone bridge, the telephone, 
magneto and other instruments, as well as the many ways of 
their application in testing for defects and for circuits in elec- 
trical installations having been given in a previous work of the 
authors (Wiring Diagrams and Descriptions) it is not thought 
necessary to repeat them here, especially as a work of this 
kind is necessarily limited in diagrams which would be re- 
quired to a full understanding of methods. This chapter will, 
therefore, consist only of such hints and instructions as apply 
to general work. 

An electric light circuit may be tested for "short circuit" by 
connecting an incandescent lamp in place of one of the fuses. 
If the lamp burns while there are no lamps in circuit, there is 
sure to be a short circuit. A low candle-power lamp will indi- 
cate with less current than a high-candle-power lamp and is, 
therefore, better. If no lamp is available a small fuse should 
first be tried. 

A test for "ground" may be made in the same way, but the 
lamp must be connected to both sides in turn and the fuse left 

000000000 o'oo 




Figure 133 

out. If the main system to which the circuit to be tested con- 
nects is not grounded, a temporary ground must be put on. 
This is best done by connecting a lamp with one wire to a gas 
or water pipe and the other to the "live" binding screw on the 
opposite side of cutout to that in which the other lamp is con- 
nected. Thus, in Figure 133, if a ground should exist at 3 and 
the lamp be connected to gas pipe, as shown, the test lamp at 1 
would burn. 



218 MODERN ELECTRICAL CONSTRUCTION. 

If a voltmeter were connected in place of either of the 
lamps, the test would be much more searching. 

With 3-wire systems no ground need be put on, as the neu- 
tral wire will always be found grounded. The lamp need be 
tried in the outside fuses only. This test will be more search- 
ing if lamps are placed in all sockets connected. 

In placing fuses in the 3-wire, 110-220 volt system, the neu- 
tral wire should always be fused first. 

By reference to Figure 134 it will be seen that while the 
neutral fuse in main blocks a is out, the two circuits of lamps 
c and d must burn in series; that is, just as much current must 
pass through one circuit as through the other. So long as 
there is an equal number of lamps in each circuit there is no 
trouble ; but should most of the lamps in one circuit be turned 
off, those remaining would have to carry all the current that 
passes through the lamps of the other circuit. This current 
would overheat them and break, or burn them out in a very 
short time. If the neutral fuse is in place, each circuit is inde- 
pendent of the other and the neutral wire only carries the 
difference in current between the two sets of lamps. In order 
to insure against a neutral fuse "blowing" first in case of 
trouble, it is generally made heavier than in the outside wires. 
When a 3-wire circuit is to be cut off, the outside fuses should 
be drawn first. 

In order to find which is the "neutral" wire, two 110 volt 
lamps are connected in series and the wires from them brought 
in contact with two of the three wires. If both lamps burn at 
full candle power we have 220 volts, which is the pressure of the 
outside wires, and, therefore, the other wire must be the neu- 
tral. If the lamps burn only at half candle power, we have 
only 110 volts and one of the wires must be the neutral. That 
wire which gives 110 volts with either one of the other two 
wires is the neutral; this wire should always be run in the 
center between the other two. 



PRACTICAL HINTS. 



219 



A test for the neutral wire can also be made by connecting 
a lamp to ground. A lamp connected this way will burn from 
either of the outside wires, but not from the neutral. 

If the neutral wire should be connected to any but the 
middle binding post of 3-wire cutouts and the outside wire 
to the other two, one-half of the lamps would be almost imme- 
diately destroyed, being subject to 220 volts, while the other 
half would burn properly. 

If a short circuit occurs, say at c, Figure 134, on one side 
of a 3-wire system and blows the neutral fuse on that side of 
the circuit, we shall have 220 volts on the lamps on the oppo- 
site side. This will quickly burn them out. Most of these 



COCO 



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a 



Figure 134 

troubles are avoided to some extent by the use of such branch 
cutouts as shown. This confines trouble of this kind to the 
mains. 

On any system having a neutral wire or a wire on one side 
grounded, if a ground on either of the other wires occurs, the 
trouble can be temporarily remedied by simply changing the 
two wires of that circuit at the cutout. This will trans- 
fer the ground to the side already grounded, so that it will 
not interfere with operation. The ground must, however, be 
cleared up at once as no grounding is ever allowed inside of 
any building. 

When strip cutouts are set horizontally and there is no 



220 MODERN ELECTRICAL CONSTRUCTION. 

bridge between opposite polarities, there will be the possibility 
of a partially melted tipper fuse sagging down and forming a 
short circuit. 

On panel boards where fuses are set too close together, the 
heat of one fuse while blowing will often blow the next fuse 
above it. 

If large jfuses are enclosed in small and very tight cabi- 
nets, the vapors formed by blowing will often cause short 
circuits. 

Before installing fuses in a "loaded" circuit, it is advisable 
to disconnect as many lights and other devices as possible. If 
there is a main switch this can easily be done. If there is no 
such switch on that part of the system, the task of placing 
fuses is somewhat hazardous ; for at the very instant that the 
second fuse touches its terminal a great rush of current will 
flow. If there happens to be a "short" on the line both fuses 
will probably blow and may burn the operator's hands and 
face severely. In order to avoid this, extremely careful manip- 
ulation is necessary. The first fuse can be placed without 
any difficulty, as there will be no current flow unless the cir- 
cuits are grounded. Before attempting to place the second 
fuse the circuits may be tested for "shorts" by placing a 
"jumper" (a piece of wire heavy enough so that it will not 
be heated by the current it is to carry) with the ends on the 
other fuse terminals. This "jumper" will complete the cir- 
cuit and, if all is in order the lights will burn. If there are 
two men, one may hold the jumper while the other places the 
fuse, but it should be placed as quickly as possible, especially 
if the circuit has a motor load, for these will be started very 
soon after the lights come on and will greatly increase the 
current. If there is but one man the jumper may be tem- 
porarily fastened to the mains. 

A jumper is not absolutely necessary even with large fuses, 
for if the last contact is made quickly and held steady, there 



PRACTICAL HINTS. 



221 



will be very little arcing; one should, however, provide all pro- 
tection possible. If a piece of asbestos is at hand, it may be 
used to cover the fuses, so as to protect the hands and face 
from melted metal. 

Before attempting to re-fuse a circuit, note condition of 
cutout block. If there is evidence of a great flash, it is very 
likely that the fuse was blown by a short circuit. If the 
blowing was caused by a slight overload or loose contact, the 
destructive effect will be much less. 

Much trouble can be prevented by cleaning terminals of 
fuse blocks occasionally and going over nuts and screws to 
see that they are tight. 

In Figure 135, a shows the proper way of connecting small 
wires into such terminals. This method prevents the screw 
from cutting into the main wire and allowing it to break. 

A wire should always be bent around the binding post of 
switch or cutout in the direction in which the nut which is to 





Figure 135 



hold it must turn to be fastened as in c. If a wire is not long 
enough to be bent around the post or screw, a small piece of 
wire should be placed opposite it so as to give a level bearing 
to nut or washer. See b. 

Plug cutouts having their metal parts projecting above the 
porcelain, as shown at d, should be connected, whenever pos- 
sible, so that these metal parts are dead when fuses are with- 
drawn. This will prevent many accidental short circuits. 

The positive and negative wires of a circuit can easily be 
determined by immersing both wires in a little water, keeping 



222 MODERN ELECTRICAL CONSTRUCTION. 

them an inch or so apart. Small bubbles will soon appear at 
the negative wire. 

If an arc lamp has been properly connected, the upper car- 
bon will be heated much more than the lower and will remain 
red longer. An arc lamp improperly connected is said to be 
burning "upside down" and will at once manifest itself by the 
strong light thrown against the ceiling. 

It is very often found necessary to determine the capacity 
of a cable which is already installed and where it is impossible 
to get at the separate wires of which it is formed. As cables 
are usually made up in a uniform manner, as shown in the 
table below, their capacity can be determined by the following 
method : To find the number of circular mils in a cable made 
up of wires of uniform size. Measure diameter of cable, 
count number of wires in outside layer, and, referring to the 
table below, find the same number in the first column; divide 
the diameter of cable by the number set opposite this in the 
second column. This will give the diameter of each wire. 
Multiply this diameter by itself and then by the number of 
wires contained in cable as given in the third column. All 
measurements should be expressed in mils (1/1,000 inch) and 
the result will be the circular mils contained in cable. 



Outside 


layer 


6 
12 
18 
24 
30 
36 
42 


wires 


3 

5 

7 

9 

11 

13 

15 


times 


diameter 


7 
19 
37 
61 
91 
127 
169 


wires 


in cable 



The various figures in Figure 136 are designed to show how 
many single wires may be run in one conduit. Under each 
figure is given a number which, if multipled by the diameter 
of the wire to be used will give the smallest diameter of 
tube which can contain the corresponding number of 
wires. Thus, for instance, if 12 wires are run through 



PRACTICAL HINTS. 



223 




224 MODERN ELECTRICAL CONSTRUCTION. 

one tube or conduit, the diameter of that conduit 
must be at least 4 1/3 times as great as the diame- 
ter of the wire to be used. Each figure illustrates 
the amount of spare room the corresponding number of wires 
leave, and it is necessary to use considerable judgment. Long 
runs will require more space, especially if the wires be quite 
large. Much also depends upon the nature of the insulation 
and the temperature. The figures are believed to be correct 
for single wires and can be followed for twin wires, as the 
same number of conductors arranged that way will not occupy 
as much space as single wires. The actual diameter of lined 
and unlined conduits are given in another table and may be 
referred to. The best way to accurately determine the diam- 
eter of small wire consists in cutting a number of short pieces 
and laying them together, then measuring over all and divid- 
ing the measurement by the number of wires. 



TRICKS OF THE TRADE. 

Cases have been known where it was requested to replace 
single pole switches by double pole, that the single pole switch 
was replaced as requested, but, instead of running^ both wires 
through it as required, only one wire had been properly 
brought into it and the other two binding posts filled out with 
short pieces of wire calculated to deceive the inspector. A 
test to detect this without disconnecting the switch is easily 
made. By reference to Figure 137 it will be seen that if a 
double pole snap switch is properly connected, current can 
be felt if the points a and h are touched with moistened fin- 
gers. If the switch is connected single pole, current can be 
felt at h and c, when the switch is open, only. 

On one occasion a wireman had run some wires on insu- 
lators along a ceiling and instead of soldering joints had care- 



TraCKS OF THE TRADE. 



fully, in many places above the joints, smoked the ceiling with 
a candle in order to deceive an inspector. 

In several cases where an "over-all" test of insulation re- 
sistance was made, meter loops which had been run in con- 
tinuous pieces were found with the wire "nicked" with a knife 
and then broken, leaving the insulation nearly intact, but the 
circuit open. A similar trick is often worked with the ground 
wire of ground detectors. 

In other cases plugs with fuses removed were put in 
"bad" circuits. In one case the real circuit wires (concealed 





Figure 137 



Figure 138 



work) were disconnected from cutouts and pushed back into 
the wall and short pieces connected instead. 

In another case where wire not up to requirements had 
been used and condemned, this wire, being run between joists 
and concealed by plastering, was pushed back and short 
pieces of approved wire stuck in at outlets. 

Sometimes in fished work after inspection the long 
pieces of loom reaching from outlet to outlet are withdrawn 
and short pieces at the outlets substituted. 

Lamp butts with wire terminals twisted together, or a 
strand of wire from lamp cord twisted around the base as 
shown in Figure 138 and screwed into the cutout are often 
used in place of fuses. The strand of cord is sometimes used 
to help out a fuse plug on an overloaded circuit. 



226 MODERN ELECTRICAL CONSTRUCTION. 

Table of Carrying Capacity of Wires. 

The following table, showing the allowable carrying ca- 
pacity of copper wires and cables of ninety-eight pe:r cent con- 
ductivity, according to the standard adopted by the American 
Institute of Electrical Engineers, mtist be followed in placing 
interior conductors. 

For insulated aluminum wire the safe carrying capacity- 
is eighty-four per cent of that given in the following tables 
for copper wire with the same kind of insulation 

TABLE NO. I. 



B. & S. G. 

18. .. 
16. . . 


Table A. 

Rubber 

Insulation. 

See No. 41. 

Amperes. 

3 

6. . . . 


Table B. 

Other 

Insulation 

SeeNos. 42 

Amperes. 

5... 

. . . . 8. . . 


to 44. 
Circ 


ular Mils. 
1,624 

2,583 


14. . . 


12 


16. . . 


4,107 


12... 

10... 

8. . . 


17 

24 

33. . . . 


23... 

32... 

46. .. 

65. . . 

77. . . 

92. .. 

110... 

131. . . 


6,530 
10,380 
16,510 


6. . . 


46. . . . 


26,250 


5. . . 
4. . . 
3... 

2 . : . 


54 

65 

76 

90 


33,100 
41,740 
52,630 
66.370 



1 107 156 83,690 

127 185 105,500 

00 150 220 133,100 

000 177 262 167,800 

0000 210 312 211,600 

Circular Mils. 

200,000 200 300 

300,000 270 400 

400,000 330 500 

500,000 .... 390 590 

600,000 450 680 

700,000 .... 500 760 

800,000 550 840 

900,000 600 920 

1,000,000 650 1,000 

1,100,000 690 1,080 

1,200,000 730 1,150 

1,300,000 770 1,220 

1,400,000. 810 1,290 

1,500,000 850 1,360 

1,600,000 890 1,430 

1,700,000 930 1,490 

1,800,000 970 1,550 

1,900,000 1,010 1,610 

2,000,000 1,050 1,670 



TABLES. 227 

The lower limit is specified for rubber-covered wires to 
prevent gradual deterioration of tlie high insulations by the 
heat of the wires, but not from fear of igniting the insulation. 
The question of drop is not taken into consideration in the 
above tables. 

The carrying capacity of Nos. 16 and 18, B. & S. gage wire 
is given, but no smaller than No. 14 is to be used, except as 
allowed under Nos. 24 v and 45 b. 



WIRING TABLES. 

The wiring tables, II-VI, are arranged in the following 
manner : For each size of wire and voltage considered there 
is given (under the proper voltage and opposite the number 
of the wire under the heading B. & S.) the distance- it will 
carry 1 ampere at a loss designated at top of page. 

The same wire will carry 2 amperes only half as far at the 
same percentage of loss and again will carry I ampere twice 
as far at double the percentage of loss. 

From these facts we deduce the rule of these tables, which 
is: Multiply the distance in feet (one leg only) by the num- 
ber of amperes to be carried. Take the number so obtained 
and under the proper, voltage find the number nearest equal to 
it. Opposite this number, under the heading B. & S., will be 
found the size of wire required. To illustrate : We have 22 
amperes to carry a distance of 135 feet and the loss to be al- 
lowed is 3 per cent at 110 volts. We therefore multiply 135 X 
22 = 2970, and turning to table IV., which is figured for 3 per 
cent loss, follow downward in the column under 110 until we 
reach the number nearest equal to 2970, which, in this case, is 
.3180 corresponding to a No. 7 wire. With this wire our loss 
will be slightly less than 3 per cent, while with No. 8 it would 
be somewhat in excess of 3 per cent. 

For three-wire systems using 110 volts on each side the 
column marked 220 volts should be used. The column marked 
440 volts is provided for three-wire systems using 220 volts 



228 ■ MODERN ELECTRICAL CONSTRUCTION. 

on each side. The sizes determined will be correct for all 
three wires in both cases. 

The columns at the right, marked motors, are arranged 
in the same way, the only difference being, for greater con- 
venience, they are figured in horse-power feet instead of am- 
pere feet. For this reason we multiply the distance in feet 
by the number of horse-power to be transmitted and divide 
by t4ie percentage of loss, all other operations remaining the 
same as under lights. When any considerable current is to 
be carried only a short distance the wire indicated by the de- 
sired loss will very likely not have sufficient carrying capacity ; 
it is, therefore, always necessary to consult the table of carry- 
ing capacities. 



RULE FOR WIRING TABLES. 

For lights, find the ampere feet (one leg) and under the 
proper voltage find the number equal to this or the next 
larger; opposite this number, in the column marked B. & 
S., will be found the size of wire required. 

For motors, proceed in the same way, using horse- 
power feet instead of ampere feet. 

For alternating currents, the results obtained by multi- 
plying the amperes (or horse-power) by the feet, should 
be multiplied by the following factors: 

1.1 for single-phase systems, all lights. 

1.5 for single-phase systems, all motors. 

For two-phase, four-wire, or three-phase, three-wire 
systems, each wire need be only one-half as large as for 
single-phase systems and the number obtained may, there- 
fore, be divided by two. 



229 



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MODERN ELECTRICAL CONSTRUCTION. 









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r-<.-l.-l(N (NCO-^iOt^ Oi y-f -^ CC C<\ 00 CD lO rf lO lO CO l> 00 l> ■* 

TH,-<,-ica (Mco'^ioco t^cooO'-ico 




o 


T)<O<M00O Tt<CO00'*(M TfiCOtN-^-* OOCOOOOO ■* (M (M Tt< oO Tfi 

(NOOiOrtHCD 005(M(M05 CD lO 0> tJH t^Jh Tt<CDO5CO00 Tt* r-( CO tH 00 00 

(MC^CO'^iO t^OO'-H'^t^ C^00>OiOr^ (Mr-iTt<»C(N o> 1> ■* --< (M lO 

^^^ Oao;CO^.O t^O^^HCOcD oo?^^^^§ 




O 


sg§§2^ s^ss^ §;^g^^ 2§^§S ^?5§§S^ 

.-ii-l i-ioq(NCOTt< lOt^OO'-H-* OOfMOOCOO t^ Tt< ,-H t^ lO T-H 

• ^^ l-^(^^(^^coTt^ tjh lo co co co t^ 










<N -t^ •■* -co -co-^ iccoot-t^ or^oico OOOOOO 

T-l -.-H -(N -co --^lO CDt^050(N lO t^ .-H CO t^ O CO CD OS lO lO 




PqO 


TtiC0(M^O C500t>COiO Ti<C0(Mr-lO OOOOO OOOOOO 

(MCO CO^TtiiOOO 










O 
<! 

O 
> 




(MTt<-*0(N OOOO'^CO (N-*(N00CO OfNtMOCD COOOOOOOOO 
I^OCOCDCO <M(M00005 05C0OOC0 Ca lO t^ (M tH lO CO C^ -"t^ O O 
CO^COCOiM COt^THl^Tt^ 05^05^^ COt>(MCO(N 00 05 CO CD ^ 00 
T-HiMiMCO'* lOCOOOOCO CD>-HCDTt<CO rf^ CO cO (N Oa (M <N CO rf b- rf 
.-Hr-I .-KMCSJCOTt* IOCOOOO(N ^CDOOOOt-i 




O 


COlMOqOcO 0^*0 (MOO CO(>JCOTt<00 OCOCOOOO OOOTt^TjHOTt* 

COIOCOOO'-I COCOTt<iO-* OSCOOSiCCO COr^COCOO (MOOCOiMOO 

OOOCOCO^ CDCO(MC0t^ '^t^THOiO ^ CO ^ rH ^ tH ^ CO CO t^ tJh 

tHifHt-KN (MCO'^iOCO 00OC0I>tH t^T^cOi-H^ .-1 i-H >-l(N CO l> 

.-lrH,-H(M (MCOThiOCO t^OOOiOOO 




o 


OOCOCOgOO 0(MOCOTt< 00CO0000Tt< OOOOOO^ ^0<N(MO(M 

i-H (N CD -"i* "O COO0(NI>t^ rtHCOT)<(N00 00 00 CO 00 lO rH rJH CO CO lO O 

■^ICCOOOO COCOi-HCOfO (NCOt^iOt^ lOrHiOiOiO l^ t^ 00 1-1 00 1^ 

-H r-<TH(M(NOO -^lOcOOOO COt^i-HiOO lOOiO^r-HCO 

.-H .-H,-l(N(MCO COTt^TtliOOO 

i-i(M 




s 


§^2g8 ^^ggg 8^§?^^ §§§^^ S2S§^^§ 

i-KNCO-^iO C0t^O(M>0 O^CrHOO rfl fH ^ O ■* 00 C^ CD i-i --KM 

,-t^~: (M(NC0Tt*iO COOOO(M'* COOl'-i'^oOCO 

'-H.-lrH .-H T-I(M (N Tt< 05 



TABLES. 



231 





ll 


1 


.002628 
.002084 
.001653 
.001311 
.001040 

.000824 
. 000654 
.000519 
.000411 
.000326 

.000259 
.000205 
.000163 
.000129 
.000102 

.000081 
. 000064 
.000051 
.0000431 
.000036 

. 0000308 

.000027 

.000024 

.0000215 

.0000108 

. 0000054 


0^ 

X 

I 


H 
O 
■< 

a 


s 


tXNOl^t^ CO^-^C<iCC '^r^iM-HO OJfOiC^LO rH t^ ,-^ lO O CO 
C0C^CCt^-<4< CDiOiOiOO r^ooot^oo aocooico iocoioo.-hoo 
r-r^i>Tt<co Tt^ost^ooo »o^GOc^(N ^^oin^ oioot^-*oo 

r^lMCNCO-* lOOOO^fO IXMt^iO-* 0^05100 r^OOOiO^C^l 
i-HrH r-i(MC^eO'^ lOt>GOOC^ -^OOOT-HCMTil 


§ 

^ 


^OiMOOO r)<cO00'*iM rt'OiM'*'* OOCOGOOO -^CMCMTtHOO^ 
TjHOOrHOOO (MI>Ot}<iO OOCOIOCDO ^Or^OCN CDt^OiOfMO 
OOO'-HCDCO (NCCt^iOt^ lOi-HiOOlTti T}<o>05-*t^ COf0iO00i>iO 
i-i^lMO^CO ■<4<«OO00O COt--^t^-* COTt<GO'-il> COOOCNiO^ 
.-H .-(^(N(NCO T}<1000005 .-HfO-^OCNiO 




OO00C-)O COTt*(MOOO CD-^GOOO OO^IMCM OOOOOO (MO 

COC^IMt^Tf* iOTf<O>CO00 O30000'-<'-< Or^Tt^iOCO .-iOTt<T-HfOt^ 

CO-*iOOOO OCOOt-HCD CO(MCOOOO OOlXMCOTt* TjH lO O t^ Tt< 00 

i-i--ii-l(N(N CO'^iOOOO OCOt^O^ 00<MOO^'.-^I 

'-H'-Hi-l(N(N (NCOCOrJHOOO 


o 


^iCKMOOO TtHOCO^iM Oir-lt^T}*-^ lOiO<-H0000 Tt* (N (M 03 00 05 

OOOCOO^ OfOfMCOI^ T}<I>TfO»0 ^fO^OOO 0-*0l>i0^ 

r-<.-l,-l(M (MfOTjHlOO OOOCOt^i-l t^^COOT-l .-h ^ ^ rH CO t^ 

^T-Hr-tiM (NCOtJ^iOO I>0005000 




c d 

66 


(M •!> -^ -CO -O-* iCCOOl>t> OI>OiOO OOOOOO 

i-H -r-l -C^ -co •■^lO COI>050(N ICI>.-HCOO OC0005»OiO 

• • • • ^rH ^^C4C^(M COCOeOMOO 




THrO(M^O OJOOt^OiC rt<C0<M-HO OOOOO OOOOOO 

(NCO CO^TjiiOCO 




IS 

o 


o 

■< 

s 

o 


o 


OOCDCOOOO 0(MOCOTt< OOOOOlM-^ OOOOOO-* '^OC^KMO'^ 
0»OCT>'*Tf< 00O3(M>O-* OOOJIOOO 00 (M O 00 !M OO^^Olt^Or; 

(MCOCO»00 1>0(M00 iO(MO^TtH .-HCOOiCOCO Tt^'^TfOr-H^ 
T-H,-lrH(N (MCO-^iOO OOOC^llOOO T-l tJH 1> o >-< 05 


o 


TjfQOOOO'* OOO00<M Tt< 00 Th r-H (N OThTjHOlM (N O O O O O 
iOI>05C^I> 05-*OiM<N TtHa>T)H00iO -^OO'^O ^(M0300»CO 
(Mi005»0.-I OSOCOO-H r^OINiOCO l>iOt^t^O TH(MTiH^io^ 
^rHrH(MfO CQIOOOOO (MOOIOIM O rH ^ O ^-l t^ CM l:^ CO »C -1 
rH ^^(M(MCO ^1001>05 OiMCOiQO^ 
^^^T-lCOO 


o 


I>050i0t^ lOCOO'*^ (MOXNiMO 0(N(MO'-^ — <OOOCO»OCO 

(N00O5CO00 OSIMOO^O t- 'i^ (N 05 l> t^ 00 IQ t^ CO t^ ^ Tt< ^ t>. lO 

Ot>05(NiO 051C-IOO C0Or-*t^^ COt^COCOOO lO — ( l> 1^ t^ iC 

r-li-l rH(NC0^»O OOOOiMCD 0»0(MOOiO CO-^GOO(MiO 

.-HrH^ (MIMCOCO^ »OC001>100 


S 


Tf*(NTt*00 (N^CO<MTtH OCOiOCOOi Tf< 05 O O O CO r^ 03 05 IM Tt< 

05t^t^0»0 -^OSOOOl Ot-iOOCO(N 00»0t^050 O)00O3I^<M-<t 

(r^COrt<OI> O5^iOO3C0 OOOt^OO CDO(MOO CO X 'i^ (N <M ^ 

T-li-H,-l(N COCO-^Ot^ O5(N'O00'-l »O00iMO(M'* 

T-lrHi-IlM (NC^COCOt^^ 



MODERN ELECTRICAL CONSTRUCTION. 





|l| 


,-1 CO IO00-* 
OOrt^fCrHO Tt<-<^05T-I0 OSiOM06(N r-4 tH i-i CO CD OI>'*'HOiO 
(N00>O^-TtH (NlO^rHfM lOOCOlMO Q0CD>C'*CO CO (M (M (M .-H O 
(OOCDCOO QOCOiC^CO (M (M rH ^ ^ OOOOO OOOOOO 

OOOOO OOOOO OOOOO OOOOO OOOOOO 
OOOOO OOOOO OOOOO OOOOO OOOOOO 


1 


s 

O 
> 


i 


«O^OCOCO •*C<J(N«0'* (M<£>CO0000 (NtHOGOO OOcDGOOO^ 
.-lOl^COOS OON.l>COTt< COlOl^fN-* CO O 00 <M 00 CO ^ O tJH 00 ^ 
COCOCOOO (N(NCDt^iO -^lOi-HOO OSOOO'^'O 01>0005002S 
(N (M CO r}< lO t^O5.-l-*Q0 C005I>t-a> tJH'^oOOOO CO^fMO^c^ 
i-Hi-HrH (N<NCO-*lO l>03<-ITt<0 O3(MiO00CD^ 

--H^tH ,-l(M(M(MlOr-H 


o 


(MOCOrt<0 (N00-*(MO CqO0CD(M(M OO00Tt<TtH (M CO CO (N tJ^ (M 
OS^i-HGOQO C0CD(MO5e0 rH Tt* CO »0 »0 O^000rt<0 »0 05 lO lO O t^ 
l>iMQ0»Ort< COi-HOCOCO i-lOOt^COOS OiC^OliOCO iCCO-^i-HCOCD 
T-<(M(MC0'4< lOOOl^Tt^ OOC^OOCOiO I^COt^OOO .-1 CO lO I^ Tt< 00 
.-H^ rHlMC^CO'* IOI>0>OCO lO l> 05 1-H CO CD 
rH,-( ,-lTHrH(MTfCO 


i 


OOO-^COO OOfNCOOC* 00(M-<*0000 OOfNCOCO 00 Tt< -rfi 00 CD 00 

^COOOCS) OOi0Tt<00 (M^OOOOOO OOOJOiCOt- Q0(MCDQ0t^CO 

■^lOt^OOt^ TtHI:^(M00iO iOO^OtH -^COOSrHiC 00-*00(NiO.-H 

i-l.-H(M<NCO -^lOt^OSi-l -^OOCNt^C^ OCOOOTt^OOt^ 

.H rH,H(M(NCO COTti'^lOOrH 


O 

1-H 


(NOCO-^O (M00(M(NCO (MOOCDIMC^ OOOO"^"* <M CD CO <M ■* !M 

"-l-^IXMOO »0-*CD'-H05 C0<MO5I>l^ (M 00 '^ 00 ■* l> lO t-H I> tJ< 0> 

^^r-iOici COTjHlOt-OO ^Tj^Ji-MOO CO>Ot-t-^ ThOO<M>OrH(M 

.-Hr-lrH(NlM CO Tt< lO CO 00 05 O (M CO t^ '^ 




C d 


(N -l^ -Tj* .fC .rortH lOcOOt^r^ OI>0>00 OOOOOO 
^ .^ .(M -CO -TtiiO CDt^050(M l01>i-HC0t^ O CO CO 05 "3 IC 


CO 6 


TjfC0<Ni-iO O5001>CD»O 'Tt<C0(NrHO OOOOO OOOOOO 

<MCO COTt<Ti*iOOO 




Oh 

S 


o 

> 


? 


■*00Q0O':}< OcDOOOiM TtHQO'^cDiM Ort^TJ^O(N (NOCOCDOCO 
Tt<001C^CD Tt<iOCD005 OOlMOO'-lt^ Tt< O ■* ■* CO i-H (M IC 0> O !i 
CO<MC01>rt< COTt<OiTtHOi a>aiO(N(M COiOiOCOT}^ l^OSCO(M00S 
CO-^iOCDOO OCOCDrHCD C0(MCO00CO 00 t>(N •* tJH lOiCCDOS-^S 
.-H r-1 i-l C^ (M CO'^iOOOO OCOt^OTji 00(NCDOr-iJo 




^^^2^ U^^^^ g^g§^ SS^gS §§?5^8§ 

CD^COCO(N OOr^-^lv* Oi-^OS'-H'-I COt^(MCO(N O0O5C0CD-*00 

r-<(N(NCO-* lOCDOOOCO CO --1 CO Tt^ CO '^ 00 CO <M (M (M C^ CO tJH t^ oO 

^r^ ^(N(MM-4< iOCDOOO(M rhCOOOOoS 


O 


^222°2'^ CDCDTt<iOTtH OSCOOmcD COt^COCOO (N 00 CO (M O O 
OOOCOcDrH CDCO(MeOt^ -^t^T|HO»0 i-HCOi-H^T-l Tt< ■<* CD CO !>. •<* 

i-lrHrH(M (^^CO':i^lOCD OOOCOt^i-H t^^COi-HrH 1-H ^ 1-H (N CO t^ 
rH,-HrH(M (M CO Th »0 CO t- 00 O O O O 


s 


(MCDCMOO CDOO-^COIM O '^ O Tt* C^ (M(NO0000 ■<# CO (M (N CD (N 

0305COOO 1000OC005 OOOOO^t^t^ i-lT-HCD(NbO CD'-HCOt^05<3l 

CO^CDOOO (MiOOiO^ OOCOO^ OS (M CO t-h 00 I^iOCOCOlMiC 

i-H i-Hi-((N(MCO '<J*iOCOOOO (NCOO-^OO COOOCOOOCOfN 

^ '^rt ^^(^,C^C^ C0CCTtHTlHOJO5 



TABLES. 



233 





111 


OOTiHCOr-^O Tj4 rt^ Oi rH CD 05 iC CO 05 (M rHrJ^^JoO O r- Tt* !2 O lo 

<y°^"5:i2; S^'S':;'^'^! •cocdcmo ooo•0'*(^: cO(M(Mc^)r-(o 

CDOCOCOO OOcOiO-*CO <M(Nr-i,-i,-i OOOCO OOOOCO 


I 

o 


o 

o 
> 


o 

s 


lOOOiOiO lOOOOO OiOOiOO iO»OiO»CiO iOiO»OiOO'« 
05<Mi005'* 00501 C^i 00 OlTtHt-OOrH ^O(>5C0(M OOOOOt-iOO 
COimOlXM >-(iCiOTtH,-i (MOl^r^GO CDiCr^iOt^ OGOOr-HCO^S 
(NCO-^iOt^ 05— I'i'OOeO OiCOCDOOfO COOOOOiOO lOOCOi-iiM?! 
^.-ir^C^ <MC0^iOI> 05r-iT}ii>^ rPOOrHiOO^ 


S 


ooooo ooooo ooooo ooooo oooooo 

Tt^OlMOOO Tt^tOOO^tN TjicDlMrt^Tt* OOCDOOGO Tt^CMO'^OO'*' 

(NOO'O'^O 003<M<N03 C!iO05TtT}< tP O 05 CO 00 ^ --( fO Tt' 00 ^ 

(NCMCOTfiiO t^OO^rJHt^ (MQ0iOiCH> (M^rPiOCM Oit-Tfr^iM^ 

rH,-lrt C<)(MCOTriO 1>05^COO OO^Tri>rt<§ 

^ ^ ^ t-4 (M C-l CJ lO r- 


o 


ooooo ooooo ooooo ooooo oooooo 

COOOOOIO O^C^OOO COrt^ODcOCD OOrt^MC^l 000000 05 

lOlXXl'-H^ l>(N00iO-!iH CO'-HOCOCO i-t03I>05r^ fOfMOOOt^'* 

.-H^ T-i(M(Mf<:'* iCt^QO^Tt* OOfMOOCOO t^ -* .H t^ lO .-h 

7-ti-t i--(M(MCOTt< Tt^iOOOCOt^ 


O 


OiOOOO OOiOOO OiOiOOO lOiOiOOO OOOiOOiO 

■*t^C^00»O -^COOOSCN lOOO-^-^OS CKMOOOOOO Tt<t^I>CDC0O 

^r-,(M<MCO rt*iCt-O0r-i Tt^^^(^^00lO iOI>^Tl^Pl Q0L0O1OO500 

,-1 ^.-i(M(M(X> Tt^iOt^OOO T-iCOiOOCOt^ 






(M -t^ .Tt< -co -OtH iOOOI>t> Ot^OiOO ■ OOOOOO 
1-1 -.-1 -(M -co -^lO C01>a50(M iCt>.-iC01> OCOOOiiOiO 

rH,-i ,-H,H <M(M(M cccoeocooo 




T^fOCM-HO O5Q01>COiO Tj<fC(NT-<0 ooooo OOOOOO 

(MM C0°^§OO 
■-KM 




i 

o 

^3 


O 

> 


o 


OOOOO OOOOO OOOOO OOOOO OOOOOO 
OOOOOg OC^OOTtH 00O^I>'* OOOQOOTfi '^OlMOlgg 

'^lOOOOO COOi-HOCO <Ml?0t>iOlr^ lOr-iiOiOiiO I> I^ 00 --^ 2 CO 
--H i-Hi-iCMfMCC TjHLOOOOO fOt^.-iiOO LOOiCi^oo 


o 


ooooo ooooo ooo>oo OOOOO oooooo 

03COC0005 >0'-I000t> -^CO-^COOI 0'*Tt<Ot^ l>OCDr-HiO'-^ 
OOC0C^(M OTt<OfOOO (M00l>CDO5 a>O5O0O3I> »Ot^^00(M!2 
(NtNCO-^iO OOOOCOO ^OCO(MCO t^»OI>t^(M 0:005100°° 

^ r-irtrt (McqfOTjHio oooooqio ttSoStcoS 

l-ll-Hi-H --H C^1(N C<) lO tM 


o 


lOiOiOOiO iO>OOOiO OiOOOO OOOOiO iOOOiOiOiO 

2;-jcDO^ csjooofo cqrHr;.c;^cD "Oi-c^iooo QoioSooaS 
oeoo^o co(Ncoo-* o-*cof005 O5O5O5O3f0 iMooioSo(>q 

^TM^CqOI CO^iOOOO 0C20;-HCD CO C^ CO M O §5 ^ ^ ?! ^ CT. 
T-l^rH(N(M CCrlHiOOt^ 000--<<N»CO 

'-I 1-1 i-H (M lO 




ooooo OiOiOOO 0»0»OiOiO OiOOOO lOiOiOiCOO 

05(N050iO t^Q0Ot>.05 0'01>10^ tJh CD »0 O ^ O rf CD CO t^ -5^ 

•-HCOOOIM 1005»0,-(05 OCOOSOt^ ,_i(m ^t- ^ ^ j:^ ^ ^ ^ Jyj ^ 

^^ rtrH(MCOCO IOCOI>0(N ooSccD oaoo^ooo 



234 MODERN ELECTRICAL CONSTRUCTION. 

It is often necessary to reinforce mains which have become 
overloaded. It is quite usual though often very incorrect, to 
choose by the table of carrying capacities a wire of such size 
that the rated capacity of it and the wire to be re-enforced 
shall be equal to the load. Small wires have proportionately 
a much greater radiating surface than larger ones and there- 
fore their carrying capacity is proportionally greater. In order 
that a wire connected in parallel with another wire shall carry 

C M. X a 

a certain current, its circular mils, must be equal • 

A 
where C. M. stands for the cross-section of the larger wire in 
circular mils and A for the current to be carried by it, while 
a is the current to be carried by the extra wire. Table No. 
VII is calculated from this rule and shows the size of wire 
necessary to re-enforce another overloaded to a certain per 
cent as indicated in the top row. For instance, a 0000 wire 
overloaded 40 per cent requires re-enforcement by a No. 1 ; a 
No. 3 wire overloaded 20 per cent requires a No. 10 wire. 
Where large wires are re-enforced in this way by smaller ones 
great care must be taken that the larger wire cannot be acci- 
dentally broken or disconnected, since in such a case the whole 
load would be forced over the smaller wire and would likely 
result in a fire. The two wires should be securely soldered 
together. 

TABLE NO. VII. 



Am- 
























peres. : 


B. &S. 


10% 


20 


30 


40 


50 


60 


70 


80 


90 


100 


210 


0000 


6 


4 


2 


1 





00 


000 


000 


0000 


0000 


177 


000 


8 


5 


3 


2 


1 





00 


000 


000 


000 


150 


00 


9 


6 


4 


3 


2 


1 








00 


00 


127 





10 


7 


5 


4 


3 


2 


1 


1 








107 


1 


10 


8 


6 


5 


4 


3 


2 


2 


1 


1 


90 


2 


11 


9 


7 


6 


5 


4 


8 


3 


2 


2 


76 


3 


12 


10 


8 


7 


6 


5 


4 


4 


3 


3 


65 


4 


14 


11 


9 


8 


7 


6 


5 


5 


4 


4 



TABLES. 



235 















•■VIS 








ep-y 0) 8]oa 3es 'sme; 








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sanioBds JOi— -aioN 






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:^;^- 


^^5^ 




55^ 


o 


P3 






A 
O 


^ 


;i 










§^ 








H 

O 
O 


;> 
g 


1 
il 


A 

a 


: : 


:i^' 


r/3 




;^^^ ;5^^ 
















as 
< 




S°o 














o 








. 


. 


:q 










® • 






M 




w • 


s : 


5^ 








o : 














<- 

P^ 




o^ 




■t>- 






a- 










H-> 


Ot 






<^^ 


•K-<i=i 


;^3 






o — «; 


ao^ 


!-Cd 










^- 












fEl 


JM 









> 


.a 
.2 ' 

2^ ^ 




on 

I 
u 
O 

1 


A 

.a 




is ■ 

OJ 0. =^ 



236 



MODERN ELECTPvICAL CONSTRUCTION. 
DIMENSIONS OF COPPER WIRE 



0)02 




is t 


Weights 


ll 






1000 feet 


Mile 




0000 


460. 


211,600. 


641. 


3,382. 


.051 


000 


410. 


168,100. 


509. 


2,687. 


.064 


00 


365. 


133,225. 


403. 


2,129. 


.081 





325. 


105,625. 


320. 


1,688. 


.102 


1 


289. 


83,521. 


253. 


1,335. 


.129 


2 


258. 


66,564. 


202. 


1,064. 


.163 


3 


229. 


52,441. 


159. 


838. 


.205 


4 


204. 


41,616. 


126. 


665. 


.259 


5 


182. 


33,124. 


100. 


529. 


.326 


6 


162. 


26,244. 


79. 


419. 


.411 


7 


144. 


20,736. 


63. 


331. 


.519 


8 


128. 


16,384. 


50. 


262. 


.654 


9 


114. 


12,996. 


39. 


208. 


.824 


10 


102. 


10,404. 


32. 


166. 


1.040 


11 


91. 


8,281. 


25. 


132. 


1.311 


12 


81. 


6,561. 


20. 


105. 


1 . 653 


13 


72. 


5,184. 


15.7 


83. 


2.084 


14 


64. 


4,096. 


12.4 


65. 


2.628 


15 


57. 


3,249. 


9.8 


52. 


3.314 


16 


51. 


2,601. 


7.9 


42. 


4.179 


17 


45. 


2,025. 


6.1 


32. 


5.269 


18 


40. 


1,600. 


4.8 


25.6 


6.645 


19 


36. 


1,296. 


3.9 


20.7 


8.617 


20 


32. 


1,024. 


3.1 


16.4 


10.566 


21 


28.5 


812.3 


2.5 


13. 


13.283 


22 


25.3 


640.1 


1.9 


10.2 


16.85 


23 


22.6 


510.8 


1.5 


8.2 


21.10 


24 


20.1 


404. 


1.2 


6.5 


26.70 


25 


17.9 


320.4 


.97 


5.1 


33.67 


26 


15.9 


252.8 


.77 


4. 


42.68 


27 


14.2 


201.6 


.61 


3.2 


53.52 


28 


12.6 


158.8 


.48 


2.5 


67.84 


29 


11.3 


127.7 


.39 


2. 


84.49 


30 


10. 


100. 


.3 


1.6 


107.3 


31 


8.9 


79.2 


.24 


1.27 


136.2 


32 


8. 


64. 


.19 


1.02 


168.5 


33 


7.1 


50.4 


.15 


.81 


214.0 


. 34 


6.3 


39.7 


.12 


.63 


271.7 


35 


5.6 


31.4 


.095 


.5 


343.6 


3G 


5. 


25. 


.076 


.4 


431.6 



TABLES. 237 

Table giving the outside diameters of rubber covered wires for use on 
voltages less than 600. 





Solid 


Solid 


Strand- 


Strand- 






B. &S 
Gauge 


Wire 


Wire 


ed Wire 


ed Wire 


Solid 


Stranded 


Single 


Double 


Single 


Double 


Twin Wire 


Twin Wires 


Braid 


Braid 


Braid 


Braid 






0000 


47-64 


54-64 


52-64 


59-64 


54-64x101-64 


59-64x111-64 


000 


41-64 


46-64 


48-64 


55-64 


46-64X 87-64 


55-64x103-64 


00 


38-64 


43-64 


43-64 


48-64 


43-64X 81-64 


48-64X 91-64 





36-64 


40-64 


40-64 


45-64 


40-64X 75-64 


45-64X 85-64 


1 


33-64 


37-64 


37-64 


42-64 


37-64X 70-64 


42-64X 79-64 


2 


29-64 


33-64 


32-64 


37-64 


33-64X 62-64 


37-64X 69-64 


3 


27-64 


31-64 


30-64 


34-64 


31-64X 58-64 


34-64X 64-64 


4 


25-64 


29-64 


27-64 


31-64 


29-64X 54-64 


31-64X 58-64 


5 


24-64 


28-64 






28-64X 52-64 




6 


22-64 


26-64 


24-64 


28-64 


26-64X 49-64 


28-64X 52-64 


8 


18-64 


22-64 


20-64 


23-64 


22-64X 41-64 


23-64X 42-64 


10 


16-64 


20-64 


18-64 


21-64 


20-64X 37-64 


21-64X 38-64 


12 


15-64 


19-64 


16-64 


20-64 


19-64X 35-64 


20-64X 36-64 


14 


14-64 


18-64 


15-64 


19-64 


18-64X 33-64 


19-64X 34-64 


16 


10-64 


13-64 






13-64X 24-64 




18 


9-64 


12-64 






12-64X 22-64 





Table giving 


the outside diameters of rubber covered 


wires for use on 


Voltages between 600 and 3500. 








Size 

B.&S. 

Gauge 


Solid 


Solid 


Strand- 


Strand- 






Wire 


Wire 


ed Wire 


ed Wire 


Solid 


Stranded 


Single 


Double 


Single 


Double 


Twin Wire 


Twin Wire 


Braid 


Braid 


Braid 


Braid 






0000 


49-64 


56-64 


53-64 


61-64 


56-64x105-64 


61-64x114-64 


000 


46-64 


53-64 


50-64 


57-64 


53-64X 99-64 


57-64x107-64 


00 


41-64 


46-64 


47-64 


53-64 


46-64X 87-64 


53-64X 99-64 





38-64 


43-64 


42-64 


46-64 


43-64X 81-64 


46-64X 88-64 


1 


35-64 


40-64 


39-64 


43-64 


40-64X 75-64 


43-64X 82-64 


2 


33-64 


38-64 


36-64 


40-64 


38-64X 71-64 


40-64X 76-64 


3 


31-64 


36-64 


34-64 


38-64 


36-64X 67-64 


38-64X 72-64 


4 


29-64 


33-64 


31-64 


35-64 


33-64X 62-64 


35-64X 66-64 


5 


28-64 


32-64 






32-64X 60-64 




6 


27-64 


31-64 


28-64 


32-64 


31-64X 58-64 


32-64X 60-64 


8 


24-64 


28-64 


26-64 


30-64 


28-64X 52-64 


30-64X 56-64 


10 


22-64 


26-64 


24-64 


28-64 


26-64X 48-64 


28-64X 52-64 


12 


21-64 


25-64 


22-64 


26-64 


25-64X 46-64 


26-64X 48-64 


14 


20-64 


24-64 


21-64 


25-64 


24-64X 44-64 


25-64X 46-64 



NOTE. — These figures are taken from data furnished by one of the largest 
manufacturers of wire and are believed to be of at least as great dimensions 
as any standard wire on the market. Judgement must be used in applying 
these dimensions as the same size wire B. & S. gauge, of different makes 
often varies considerably in outside diameter. 



238 



MODERN ELECTRICAL CONSTRUCTION. 



Outside Diameters of Rubber 
Covered Cables. 



Outside Diameters of Weather- 
proof Wire. 



Capacity in 


Diameter 


Cir. Mils. 


over Braid 


1,500,000 


113-64 


1,250,000 


107-64 


1,000,000 


97-64 


950,000 


95-64 


900,000 


94-64 


850,000 


93-64 


800,000 


89-64 


750,000 


87-64 


700,000 


83-64 


650,000 


81-64 


600,000 


79-64 


550,000 


76-64 


500,000 


73-64 


450,000 


68-64 


400,000 


66-64 


350,000 


64-64 


300,000 


61-64 


250,000 


59-64 



Dimensions of Unlined Conduit. 



Nominal 


Actual 


Internal 


Internal 


Diam. 


Diam. 


Inches. 


Inches. 


X 


17-64 


1 


23-64 


a 


31-64 


1 


40-64 


1 


52-64 


1 


67-64 


u 


88-64 


H 


103-64 


2 


132-64 


2i 


157-64 


3 


196-64 



Actual 
External 
Diam. 

Inches. 



26-64 

35-64 

43-64 

54-64 

67-64 

84-64 

106-64 

122-64 

152-64 

184-64 

224-64 



Thick- 
ness of 
Walls 
Nearest 
64th 



4-64 

5-64 

6-64 

6-64 

7-64 

8-64 

9-64 

9-64 

10-64 

13-64 

13-64 





Outside Diameters. 


Size of 






Wire 


Solid 


Stranded 


1,000,000 




108-64 




900,000 





103-64 


800,000 


. 


100-64 


700,000 





94-64 


600,000 




85-64 




500,000 





80-64 


450,000 





76-64 


400,000 





73-64 


350,000 





64-64 " 


300,000 





62-64 


250,000 




58-64 




0000 


50-64 


55-64 


000 


47-64 


51-64 


00 


39-64 


43-64 





36-64 


39-64 


1 


32-64 


35-64 


2 


30-64 


33-64 


3 


27-64 


30-64 


4 


25-64 


28-64 


5 


22-64 


24-64 


6 


20-64 


22-64 


8 


17-64 


18-64 


10 


16-64 




12 


14-64 




14 


12-64 




16 


10-64 




18 


8-64 





Dimensions of Lined Conduit 



Nominal 


Actual 


Actual 


Internal 


Internal 


External 


Diameter 


Diameter 


Diameter 


Inches 


Inches 


Inches 


i 


32-64 


54-64 


f 


45-64 


67-64 


1 


58-64 


84-64 


u 


80-64 


106-64 


n 


90-64 


122-64 


2 


115-64 


152-64 


2\ 


144-64 


184-64 


3 


176-64 


224-64 



TABLES. 
DIMENSIONS OF PORCELAIN KNOBS. 



239 



Trade 

No. 


Height 


Diameters 


Hole 


Groove 


Height of 
Wire 





2i 


3 


11 


1 


-h 


1 


3 


2J 


•jL 


f 


If 


2 


2 




i 




1 


3 


li 


9 


jL 


■jL 


f 


Si 


2 


2 


iT 


T^ 


1 


4 


IH 


lo 


1 


1 


i 


4* 


IJ 




§ 


^ 


1 


5 


U 


■^ 


i 


A 


f 


f* 


4 


I- 


i 
1 


2 


1 


9 


11 


1 


A 


t4 


f 


10+ 


If 


If 


f 




1 



DIMENSIONS OF GLASS KNOBS. 



Trade 
Number 


Height 


Width 


Size of 
Hole 


Size of 
Groove 


1 


1+ 


n 




3 


1+ 


H 


n 


f 


1 


2 


If 


2 




"3^ 


3 


2i 


2 


f 


■3^ 


7 


21 


2 






8 


3f 


2f 




1" cable 



SIZES OF PORCELAIN TUBES. 



Internal 


Shortest 


Greatest 


Outside 


Diameter 


Length 


Length 




Inches 


Obtainable 


Obtainable 




_5^ 


i 


24 


_9_ 


J 


i 


24 


rk 


1 

1 


24 
24 


2 


1 


24 


13 


i 


1+ 


24 


1^ 


li 


2| 


24 


Iff 


1+ 


2+ 


24 


2^ 


If 


2i 


24 


2:^ 


2 


2* 


24 


211 


2} 


2+ 


24 


3t^ 


2| 


24 


24 


3ii 



DIMENSIONS OF MOULDINGS. 



Size of Groove 


Size of Wire 


Size of Groove 

3-4 

7-8 
1 
1 1-4 


Size of Wire 


7-32 

5-16 

13-32 

9-16 


14-12 B. & S. 

10- 8 B. & S. 

6-5-4 B. & S 

3-2-1-0 B. & S. 


0-0000 Stranded 
250.000 C. M. 
500.000 C. M. 
750.000 C. M. 



240 MODERN ELECTRICAL CONSTRUCTION, 

DIMENSIONS OF CLEATS. 



One-Wire Cleats. 
DuGGAN Cleat. 

No. 4 holds wires 16-8 B. & S. 

No. 7 

2-00 

000-300,000 C M. 

400,000-800,000 C. M. 

900,000-1,200,000 C. M, 



No. 5 
No. 6 
No. 8 
No. 



Brunt Cleat. 
Stand. 
Number Width Length Groove 

328 f 2 ^ holds wires 16-5 B. & S 

329 1 2i i " " 8-3 

331 -11 21 H " " 3-00 

330 1| 2-h \ " '• 4-1 

332 li 2| H " " 0-0000 



Two AND Three-Wire Cleats. 
Brunt. 

No. 334 2-wire holds wires 16-8 B. & S. 

No. 337 3 wire " " 16-8 B. & S 

DuGGAN. 

No. 3 2-wire holds wires 16-8 B. & S. 

No. 2 2-wire " " 6-00 B. & S. 

No. 1 3 wire " " 16-8 B. & S. 

Pass & Seymour. 

No. A-3 2-wire holds wires 14-12 B. & S. 

No. 3 2-wire " " 14- 6 B. & S- 

No. A-43 3-wire " " 14-12 B. & S. 

No. 43 3-wire " " 14- 6 B. & S. 



TABLES. 
DIMENSIONS OF IRON SCREWS. APPROXIMATE. 



241 



Trade Number 


Diameter in 


Nearest B. & S. 


Greatest Length 




tractions 


Gauge 


Obtainable 





tU 


15 


1 


1 


tSs 


14 




b\ 


12 


|. 


3 


A 


11 


li 


4 


i,~ 


9 


1 


5 




8 


2t 


6 


i/h 


7 


;; 


7 


iz\ 


7 


3 


8 


3Z 


6 


4 


9 


ki 


5 


4 


10 


12 


5 


4 


11 


el 


4 


4 


12 


27 


4 


6 


13 


j29g 


3 


6 


14 


15 


3 


6 


15 


i 


2 


6 


16 




2 


6 


17 




1 


6 


18 


hi 


1 


6 



DIMENSIONS OF COMMON NAILS. APPROXIMATE. 



Trade 


Diameter in 


Nearest B. & S. 


Length in 


No. 


Number 


Fractions 


Gauge 


Inches 


per lb. 


2d 




13 


1 


875 


3d 




12 


It 


565 


4d 




10 


U 


315 


5d 




10 


H 


270 


6d 


7 


9 


2 


180 


7d 


B¥ 


9 


2* 


160 


8d 


TZg 


8 


22 


105 


9d 




8 


22- 


95 


lOd 


t¥s 


7 


3 


70 


12d 


t¥. 


6 


3f 


60 


16d 


^\ 


6 


3i 


50 


20d 


t¥b 


4 


4 


30 



Fine Nails 



2d 
3d 
4d 



lis 
rz5 



1350 
770 
470 



MODERN ELECTRICAL CONSTRUCTION. 

RATING OF MOTORS. 
Full Load Currents. 



H. P. 


110 VOLTS 


220 VOLTS 


500 VOLTS 




* 


1.9 


.95 


.42 






2.7 


1.35 


.62 




i 


5. 


2.50 


1.15 




a 


7.5 


3.75 


1.70 






9.2 


4.60 


2.10 




2 


17.5 


8.75 


4. 




3 


24.6 


12.30 


5.60 




4 


32. 


16. 


7.50 




5 


40. 


20. 


9.20 




^ 7i 


57. 


28.5 


13. 




10 


76. 


38. 


17.5 




15 


110. 


55. 


25. 




20 


144. 


72. 


34. 




25 


176. 


88. 


40. 




30 


210. 


105. 


49. 




35 


250. 


125. 


57. 




40 


280. 


140. 


65. 




45 


320. 


160. 


75. 




50 


350. 


175. 


80. 




60 


430. 


215. 


100. 




75 


520. 


260. 


120. 




100 


700. 


350. 


160. 




125 


880. 


440. 


210. 




150 


1056. 


530. 


245. 




175 


1230. 


615. 


280. 




200 


1400. 


700. 


325. 





RATING OF INCANDESCENT LAMPS. 




no VOLTS 


220 VOLTS 


C. P. 


Watts 
18 


Amperes 


C. P. 


Watts 


Amperes 


4 


.16 


8 


36 


.16 


6 


24 


.22 


10 


45 


.20 


8 


30 


.27 


16 


64 


.29 


10 


35 


.32 


20 


76 


.35 


12 


40 


.36 


24 


90 


.41 


16 


56 


.51 


32 


122 


.55 


20 


70 


.64 


50 


190 


.86 


24 


84 


.76 








32 


112 


1.00 








50 


175 


1.60 









TABLES. 243 

The Hewitt-Cooper Mercury Vapor lamp requires a current of about 3.5 
amperes. 

The Nernst lamp consumes 88 watts per glower; for a 6 glower, 110 volt 
lamp, about 4.8 amperes. 

Series miniature lamps, operated 8 in series, on 110 volts, require a current 
of about .33 amperes for 1 candle power lamps, and 1 ampere for 3 candle 
power lamps. 



Tables showing the currents which will fuse wires of different sub- 
stances. 



B. &S. 
Gauge 


Diam. 


Copper 


Aluminum 


German 
Silver 


Iron 


10 
12 
14 


102. 
81. 
64. 


333. 
236. 
165.7 


246.5 
174.4 
122.8 


170. 
120.5 
84.6 


102.3 
72.6 
50.9 


16 
18 
20 


51. 
40. 
32. 


117.7 
81.9 
58.5 


87.1 
60.7 
43.4 


60.1 
41.8 
29.9 


36.1 
25.2 
18. 


22 
24 
26 


25.3 

20. 

16. 


41.1 
28.9 
20.7 


30.5 
21.5 
15.3 


21.0 
14.8 
10.6 


12.4 
8.9 
6.4 


28 
30 
32 


12.6 
10. 

8. 


14.5 

10.2 

7.3 


10.7 
7.6 
5.4 


7.4 
5.2 
3.7 


4.5 
3.1 
2.3 


34 
36 


6.3 
5. 


5.1 
3.6 


3.8 

2.7 


2.6 
1.8 


1.6 
1.1 



INDEX 



Page. 

Acid Fumes 76-137 

Alternating Current System 85 

Amperes 13 

Arc Lamps, Construction of 209 

Arc Lamps, Installation of 108-113-167 

Arc Lamp Switches 109 

Armored Cable 181 

Base Frames, Generators and Motors 47-63 

Batteries, Storage or Primary 27-76 

Bells 19 

Binding Screws, Not to Bear Strain 166 

Bonds, Rails in Car Houses 169 

Boxing, Where Necessary 111-133-171 

Burrs and Fins, Fixture Work 161 

Bushings for Wires 97-185 

Bushings, Lamp Sockets 166 

Bus Bars 52-54 

Cabinets for Cut-Outs 123-202 

Cable, Armored 181 

Calculation of Wires 40 

Care and Attendance 59 

Car Houses 169 

Carrying Capacity Table . . . 226 

Car Wiring 169 

Ceiling Fans 75-160 

Central Stations 47 

Circular Mil 40 

Circuit Breakers, Construction of 194 

Circuit Breakers, Installation of 51-73-76-105-114-123 

Circuit, Open 9 

Circuit, Closed 9 

Circuits, Divided 16 

Cleats 93-186 

Compensator Coils 168 

Conductors 10 

Concealed Wiring 98-128-131-138 

Condensers 211 

Conductors (See Wires) 

Conduits, Installation of 147 

Conduits, Lined Metal 182 

Conduits, To Be Marked 182 

Conduits, Unlined Metal 183 

<^onduits, Wire for « 180 

Conduit Work 141 

Constant Current Systems 32-108 



INDEX 

Constant Potential Systems 33-114 

Coulomb 13 

Converters (See Transformers) 

Current 7-18 

Currents for Motors 65 

Cut-Out Cabinets 15T)-107-123-2()2 

Cut-Outs, Construction of lJ)i 

Cut-Outs, Installation of 105-114 

Cut-Outs, To Be Double Pole 105 

Decorative Lighting Systems 1 68 

Distance Between Conductors, Inside 111-136-141 

Distance Between Conductors, Outside 78 

Drip Loops at Service Entrance 80-116 

Dynamo Rooms 47 

Economy Coils 168 

Electric Gas Lighting 215 

Electric Heaters 129 

Electro-Magnetic Devices for Switches 114 

Electro-Motive Force 11 

Electrolysis 100 

Equalizers 50 

Extra High Potential Systems , 172 

Feeders, Railway. 169 

Fished Wires 133-142 

Fittings and Materials 17 8 

Fixtures 158 

Fixture Wire J 79 

Fixture Wiring 146 

Flexible Cord, Construction of 177 

Flexible Cord, Construction of, Heaters 179 

Flexible Cord, Construction of, Pendants 178 

Flexible Cord, Construction of. Portables 178 

Flexible Cord. Use of 165 

Flexn))o Tubing 142 

Foreign Currents, Protection Against 218 

rV)rmula for Soldering Fluid 95 

Fuses, Construction of 199 

Fuses, Installation of 114-221 

Gas Liahting, Electric 215 

Generators 47 

Ground Connections 90-154 

Ground Detectors 59-62 

Grounded Trolley Circuits 170 

Grounding Low Potential Circuits 88 

Grounding of Dynamo and Motor Frames 47-63 

Grounds. Testing for 59 

Ground Wire for Lightning Arresters 57-213 

Hanger Boards, Construction of 208 

Hansrer Boards. When Not Used 113 

Heaters. Electric 129 

High, Constant Potential Systems 170 

II 



INDEX 

Incandescent Lamps as Resistances 56-168 

Incandescent Lamps in Series Circuits 114-168 

Induction Coil 25 

Inside Worlj 92 

Insulators 10 

Insulating Joints, Construction of 209 

Insulating Joints, When Required 158 

Insulation of Trolley Wires 82 

Insulation Resistance 61-216 

Interior Conduits (See Conduit) 

Joints in Conductors 80-93 

Joints, Insulating (See Insulating Joints) 

Knob and Tube Work 93 

Lamps, Arc (See Arc Lamps) 

Lamps, Incandescent Series 114-168 

Lightning Arresters, Construction of 212 

Lightning Arresters, Installation of 57 

Lights from Trolley Circuits 170 

Loop System 143 

Low Potential Systems 131 

Mechanical Injury, Protection Against 111-138-171 

Motors 63 

Moulding, Construction of 185 

Moulding Work 138 

Moving Picture Machines 216 

Multiple Series System 34-74 

Ohms Law 13 

Ohm 12 

Oily Waste 59 

Open Wiring 135 

Outlet Boxes 149-184 

Outside Work 78-83-86-88 

Panel Boards 201 

Picture (Moving) Machines 216 

Pole Lines 81 

Portable Conductors 178 

Power 14 

Power from Trolley Circuits 170 

Practical Hints 217 

Protective Devices, Signal Circuits 213 

Railway Power Plants 76 

Reactive Coils 211 

Reinforcing Wires 120 

Resistance 12-41 

Resistance Boxes, Construction of 210 

Resistance Boxes, Installation of 55 

Tf'-slstar'ce for Arc Lamp, Low Potential 168 

Rheostats (See Resistance Boxes) 

Ill 



INDEX 

Sag in Outside Wires 79 

Series Arc System 32 

Series Lamps 168-171 

Series Multiple System 35-74 

Service Blocks and Wires 78 

Service Switcties 124 

Signaling- Systems 213 

Sockets, Construction of 205 

Sockets, Installation of 163 

Soldering Fluid Formula 95 

Spark Arresters, Construction of 209 

Spark Arresters, When Required 113-168 

Square Mil 40 

Starting Boxes 67-71 

Stations, Central 47 

Static Electricity, Overcoming 50 

Storage Battery Rooms 76 

Switch Boards 53 

Switches, Construction of 188 

Switches, Electro-Magnetic 114 

Switches, Installation of 105-124 

Switches. To Be Double Pole 105 

Switches, When May Be Single Pole 65-126 

Systems, Constant Current 108 

Systems, Constant Potential 114 

Systems, Extra High, Constant Potential 172 

Systems, High, Constant Potential 170 

Systems, Low, Constant Potential 114 

Tables ... 229 to 243 

Tablet Boards 991 

Telegraph, Telephone and Other Signal Circuits.!!". 213 

Telephones 23 

Testing '.'.'.'.'.'.'.'. 59-162-217 

Three Wire System 33-117-121-131-218 

Transformers in Central Stations 77 

Transformers, Construction of ! ! . ! ! 212 

Transformers, Inside ! ! 17^ 

Transformers, Outside !!!!!!! 86 

Transmission, Electric !!.!!! 36 

Transmission Lines, Over 5,000 Volts !.!!!!!! 83 

Tricks of Trade 224 

Trolley Circuits, Grounded 170 

Tubes, Insulating 97-185 



Volt 



11 



W^att 15 

Wire, Concentric 181 

Wire, Conduit ! ! igo 

Wire, P^'ixture I79 

Wire, Insulation of I73 

Wire, Netting Required on Arc Lamps 113-168 

Wire, Rubber Covered I73 

IV 



INDEX 

Wire, Slow Burning 176 

Wire, Slow Burning, Weather Proof 175 

Wire, Weather Proof 177 

Wires, Car Work 169 

Wires, Carrying Capacity, Table 226 

Wiring Tables 227 

Wires, Central Stations 52 

Wires, Concealed Knob and Tube Work 141 

Wires, Conduit Work 141 

Wires, Number in Conduit 222 

Wires, Distance Between Inside 111-136-137-141 

Wires, Distance Between Outside 78 

Wires, Dynamo Rooms 52 

Wires, Extra High Potential 172 

Wires, Fished 133-142 

Wires, Fixture Work 146 

Wires, Low Potential, General Rules 131 

Wires, Ground Return 83 

Wires, High Potential 170 

Wires, Inside, Constant Current 108 

Wires, Inside, General Rules ■ 92 

Wires, Undergrovmd 104 

Wires, lyToulding Work 138 

Wires, Open Work, Damp Places 137-164 

Wires, Open Work, Dry Places 135 

Wires, Outside, Overhead 78-83 

Wires, Service 78 

Wires, Signal 21 '^ 

Wires, Trolley 82 

Wiring Systems 117 



THE MOST IMPORTANT BOOK ON ELECTRICAL CONSTRUCTION 

WORK FOR ELECTRICAL WORKERS EVER PUBLISHED. 

NEW 1904 EDITION. 

MODERN WIRING 
DIAGRAMS AND DESCRIPTIONS 

A Hand Book of practical diagrams and 
information for Electrical Workers. 

By HENRY C. HORSTMANN and 
VICTOR n. TOUSLEY 
Expert Electricians. 

This grand little Tolume noc only tells 
you how to do it, but it shows you. 

The book contains no pictures of 
bells, batteries or other fittings ; you can 
see those anywhere. 

It contains no Fire Underwriters' 
rules; you can get those free anywhere. 
It contains no elementary considera- 
tions ; you are supposed to know what 
an ampere, a volt or a "short circuit" 
is. And it contains no historical matter. 
All of these have been omitted to 
make room for "diagrams and de- 
scriptions" of just such a character as 
workers need. We claim to give all 
that ordinary electrical workers nee(3, 
and nothing that they do not need. 

It shows you how to wire for call and alarm bells. 

For burglar and fire alarm. 

How to run bells from dynamo current, 

How to install and manage batteries. 

How to test batteries. 

How to test circuits. 

How to wire for annunciators; for telegraph and gas lighting. 

It tells how to locate "trouble" and "ring out" circuits. 

It tells about meters and transformers. 

It contains 30 diagrams of electric lighting circuits alone. 

It explains dynamos and motors ; alternating and direct current. 

It gives ten diagrams of ground detectors alone. 

It gives "Compensator" and storage battery installation. 

It gives simple and explicit explanation of the "Wlieatstune" Bridge 
and its uses as well as volt-meter and other testing. 

It gives a new and simple wiring table covering all voltages and all 
losses or distances. 

16mo., 160 pages, 200 illustrations; full leather binding, ^-| C/^ 

PRICE ^l.Ovy 




round corners, red edges. Size 4x6, pocket edition. 



Sold by booksellers generally or sent postpaid to any address 
upon receipt of price. 

FREDERICK J. DRAKE & COMPANY 

PUBLISHERS 
2II-2I3 East Madison Street CHICAGO, U.S.A. 



DYNAMO TENDING 




ENGINEERS 

Or, ELECTRICITY 
FOR STEAM ENGINEERS 

By HElNfRY C. :EZ0RSTMANN and 
VICTOR H. TOUSLEY, 
Authors of "Modern Wiring Diagrams and 
Descriptions for Electrical Workers." 



This excellent treatise is written by- 
engineers for engineers, and is a clear 
and comprehensive treatise on the prin- 
ciples, construction and operation of 
Dynamos, Motors, Lamps, Storage Bat- 
teries, Indicators and Measuring Instru- 
ments, as well as full explanations of the 
principles governing the generation 
of alternating currents and a descrip- 
tion of alternating current instruments and machinery. There are 
perhaps but few engineers who have not in the course of their labors 
come in contact with the electrical apparatus such as pertains to light 
and power distribution and generation. At the present rate of increase 
in the use of Electricity it is but a question of time when every steam 
installation will have in connecton with it an electrical generator, even 
in such buildings where light and power are supplied by some central 
station. It is essential that the man in charge of Engines, Boilers, 
Elevators, etc., be familiar with electrical matters, and it cannot well 
be other than an advantage to him and his employers. It is with a view 
to assisting engineers and others to obtain such knowledge as will enable 
them to intelligently manage such electrical apparatus as will ordinarily 
come under their control that this book has been written. The authors 
have had the co-operation of the best authorities, each in his chosen field, 
and the information given is just such as a steam engineer should know, 
To further this information, and to more carefully explain the text, 
nearly 100 illustrations are used, which, with perhaps a very few excep- 
tions, have been especially made for this book. There are many tables 
covering all sorts of electrical matters, so that immediate reference can 
be made without resorting to figuring. It covers the subject thoroughly, 
but so simply that any one can understand it fully. Any one making a 
pretense to electrical engineering needs this book. Nothing keeps a man 
down like the lack of training; nothing lifts him up as quickly or as 
surely as a thorough, practical knowledge of the work he has to do. This 
book was written for the man without an opportunity. No matter what 
he is, or what work he has to do, it ^ives him just such information 
and training as are required to attain success. It teaches just what 
the steam engineer should know in his engine room about electricity. 
18mo, Clotli, 100 Illustrations. Size 514x7^. PRICE NET ^1 Pn 
Sold by bookseller s generally, or sent, all charges paid, upon ^pgUU 
receipt of price - 

FREDERICK J. DRAKE d COMPANY 

Publishers of Self -Educational Books for Meclianics 

211-213 East Madison Street CHICAGO, U,S.A. 




Easy Electrical Experiments 
and How to Make Them 

By L. P. DICKINSON 

This is the very latest and most 
valuable work on Electricity for the 
amateur or practical Electrician pub- 
lished. It gives in a simple and 
easily understood language every 
thing you should know about Gal- 
vanometers, Batteries, Magnets, In- 
duction, Coils, Motors, Voltmeters, 
Dynamos, Storage Batteries, Simple 
and Practical Telephones, Telegraph 
Instruments, Rheostat, Condensers, Electrophorous, 
Resistance, Electro Plating, Electric Toy Making, etc. 
The book is an elementary hand book of lessons, 
experiments and inventions. It is a hand book for 
beginners, though it includes, as well, examples for 
the advanced students. The author stands second to 
none in the scientific world, and this exhaustive work 
will be found an invaluable assistant to either the 
Student or mechanic. 

Illustrated with hundreds of fine drawings; printed 
on a superior quality of paper. 

{2mo Cloth* Price, $t«25. 

Sent postpaid to any address upon receipt of price. 

FR.EDER.ICK J. DRAKE ®. CO. 

PUBLISHERS 

9 9^^ Chicagd 



A BOOK EVERY ENGINEER AND ELECTRICIAN 
SHOULD HAVE IN HIS - POCKET. A COMPLETE 
ELECTRICAL REFERENCE LIBRARY IN ITSELF 

NEW EDITION 

H6e Handy Vest-Pocket 

ELECTRICAL 
DICTIONARY 

BY WM. L. WEBER, M.E. 




ILLUSTRATED 

CONTAINS upwards of 4,800 words, 
terms and phrases employed in the 
electrical profession, with their 
definitions given in the most concise, 
lucid and comprehensive manner. 

The practical business advantage 
and the educational benefit derived 
from the ability to at once understand 
the meaning of some term involving 
the description, action or functions of 
a machine or apparatus, or the physi- 
cal nature and cause of certain phe- 
nomena, cannot be overestimated, and 
will not be, by the thoughtful assidu- 
ous and ambitious electrician, because 
he knows that a thorough understand- 
ing, on the spot, and in the presence 
of any phenomena, effected by the aid 
of his little vest-pocket book of refer- 
ence, is far more valuable and lasting 
in its impression upon the mind, than 
any memorandum which he might 
make at, the time, with a view to the 
future consultation of some volumin- 
ous standard textbook, and which is 
more frequently neglected or.f orgotten 
than done. 

The book is of convenient size for 
carrying in the vest pocket, being only 
2% inches by 51^ inches, and 34 inch 
thick; 224 pages, illustrated, and 
bound in two different styles: 

Goth, Red Edges, Indexed . . 25c 
Full Leather, Gold Edges, Indexed, 50c 

Sold by booksellers generally or sent postpaid to any address upon receipt 
of price. 

FREDERICK J. DRAKE & COMPANY 

Publishers of Self-Educational Books for Blechanics 
ai 1-213 E. MADISON ST. CHICAGO, U.S.A 



New Editioiv. 
New Edition. 



BOOKKI^BPING 
SELF-TAUGHT 




By PHILLIP C. GOODWIN 



i 

FE W, if any of of the technical works.i 
which purport to be self -instructing^ 
have justified the claims made for* 
them, and invariably the student 
either becomes discouraged and abandons 
his purpose and aim, or ne is compelled to 
enlist tne olfices of a professional teacher,* 
vrhich in the great majority of instances is' 
impracticable when considered in relation 
to the demands upon time and the condi- 
tion of life to which the great busy public i? 
subjected. 

Mr. Goodwin's treatise on Bookkeeping 
is an entirely new departure from all 
former methods of self -instruction and one 
which can be studied systematically and 
alone by the student with quick and 
permanent results, or taken up in leisure 
moments with an absolute certainly of ac- 
quiring the'science in a very short uime and 
with little effort. The book is both a 
marvel of skill and simplicity. Every 
featuie and every detail leading to the 
elimax of scientific perfection are so thor- 
ougliJy complete in this logical procedure 
and the analysis so thorough and deltly made that the self -teaching 
student is led by almost imperceptabie, but sure and certain steps to 
the basic principles of the science, whicn the author in a most compre- 
hensive and lucid style lays bare to intelligence of, even the most 
mediocre order. 

The work is the most masterly exposition of the scientific principles of 
Bookkeeping and their practical application which has ever appeared in the 
English language, and it should be in the hands of every school boy or girl, 
every clerk, farmer, teacher and business or professional man; for a 
knowledge of Bookkeeping, even tlmutrh it may not-be followed as a pro- 
fession, is a necessity felt by every person in business life and a recognized 
prime factor of business siiccess. , 

In addition to a very simple yet elaborate explanation in detail of tne 
systems of both single and double entry Bookkeeping, beginning with the 
jiaitial transactions and leading the student along to the culminating exhibib 
of the balance sheet, the work contains a glossai'y of all the commercial 
terms employed in the business world, together with accounts in illustra"] 
tion, exercises for practice and one set of books completely written up. 

J2mo Cloth. Price $J.OO. 

Sent postpaid to any address upon receipt of price. 

Frederick J. Drake & Co., Publishers 
21213 EAST MADISON ST., CHICAGO 



NOTICE 



To the many workraen who are purchasing the publications under the 
authorship of Fred T. Hodgson, and who we feel sure have been benefited 
by his excellent treatises on many Carpentry and Building subjects, we 
desire to inform them that the following list of books have been published 
since 1903, thereby making them strictly up-to-date in every detail. All of 
tbe newer books bearing the imprint of Frederick J. Drake & Co. are modern 
in every respect and of a purely self-educational character, expressly issued 
for Home Study. 

PRACTICAL USES OF THE STEEL SQUARE, two volumes, over 500 
pages, including 100 perspective views and floor plans of medium- 
priced houses. Cloth, two volumes, price $2.00. Half leather, 
price $3.00. 

MODERN CARPENTRY AND JOINERY, 300 pages, including 50 house 
plans, perspective views and floor plans of medium and low-cost 
houses. Cloth, price $1.00. Half leather, price $1.50. 

BUILDERS' ARCHITECTURAL DRAWING SELF-TAUGHT, over 350 
pages, including 50 house plans. Cloth, price $2.00. Half leather, 
price $3.00. 

MODERN ESTIMATOR AND CONTRACTORS' GUIDE, for pricing build- 
ers' work, 350 pages, including 50 house plans. Cloth, price $1.50. 
Half leather, price $2.00. 

MODERN LOW-COST AMERICAN HOMES, over 200 pages. Cloth, prior 
$1.00. Half leather, price $1.50. 

PRACTICAL UP-TO-DATE HARDWOOD FINISHER, over 300 pages. 
Cloth, price $1.00. Half Leather, price $1.50. 

COMMON SENSE STAIR BUILDING AND HANDRAILING, over 250 
pages, including perspective views and floor plans of 50 medium-priced 
houses. Cloth, price $1.00. Half leather, price $1.50. 

STONEMASONS' AND BRICKLAYERS' GUIDE, over 200 pages. Cloth, 
price $1.50. Half leather, price $2.00. 

PRACTICAL WOOD CARVING, over 200 pages. Cloth, price $1.50. Half 
leather, price $2.00. 

Sold by booksellers generally, or sent, all charges paid, upon receipt of 
price, to any address in the world. 

FREDERICK J. DRAKE & CO. 

Publishers 

211=213 E. Madison St., Chicago, U. S. A. 



m 



5 l9Cb 



